| Message ID | 20240816020723.771196-1-ying.huang@intel.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Resource: fix region_intersects() for CXL memory | expand |
On Fri, 16 Aug 2024 10:07:23 +0800 Huang Ying <ying.huang@intel.com> wrote: > On a system with CXL memory installed, the resource tree (/proc/iomem) > related to CXL memory looks like something as follows. > > 490000000-50fffffff : CXL Window 0 > 490000000-50fffffff : region0 > 490000000-50fffffff : dax0.0 > 490000000-50fffffff : System RAM (kmem) > > When the following command line is run to try writing some memory in > CXL memory range, > > $ dd if=data of=/dev/mem bs=1k seek=19136512 count=1 > dd: error writing '/dev/mem': Bad address > 1+0 records in > 0+0 records out > 0 bytes copied, 0.0283507 s, 0.0 kB/s > > the command fails as expected. However, the error code is wrong. It > should be "Operation not permitted" instead of "Bad address". And, > the following warning is reported in kernel log. > > ioremap on RAM at 0x0000000490000000 - 0x0000000490000fff > WARNING: CPU: 2 PID: 416 at arch/x86/mm/ioremap.c:216 __ioremap_caller.constprop.0+0x131/0x35d > ... > Presumably we want to fix earlier kernels? If so, are you able to identify a suitable Fixes: target? Possibly 974854ab0728 ("cxl/acpi: Track CXL resources in iomem_resource")?
Huang Ying wrote: > On a system with CXL memory installed, the resource tree (/proc/iomem) > related to CXL memory looks like something as follows. > > 490000000-50fffffff : CXL Window 0 > 490000000-50fffffff : region0 > 490000000-50fffffff : dax0.0 > 490000000-50fffffff : System RAM (kmem) > > When the following command line is run to try writing some memory in > CXL memory range, > > $ dd if=data of=/dev/mem bs=1k seek=19136512 count=1 > dd: error writing '/dev/mem': Bad address > 1+0 records in > 0+0 records out > 0 bytes copied, 0.0283507 s, 0.0 kB/s > > the command fails as expected. However, the error code is wrong. It > should be "Operation not permitted" instead of "Bad address". And, > the following warning is reported in kernel log. > > ioremap on RAM at 0x0000000490000000 - 0x0000000490000fff > WARNING: CPU: 2 PID: 416 at arch/x86/mm/ioremap.c:216 __ioremap_caller.constprop.0+0x131/0x35d > Modules linked in: cxl_pmem libnvdimm cbc encrypted_keys cxl_pmu > CPU: 2 UID: 0 PID: 416 Comm: dd Not tainted 6.11.0-rc3-kvm #40 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 > RIP: 0010:__ioremap_caller.constprop.0+0x131/0x35d > Code: 2d 80 3d 24 6a a1 02 00 75 c1 48 8d 54 24 70 48 8d b4 24 90 00 00 00 48 c7 c7 40 3a 05 8a c6 05 07 6a a1 02 01 e8 a3 a0 01 00 <0f> 0b eb 9d 48 8b 84 24 90 00 00 00 48 8d 4c 24 60 89 ea 48 bf 00 > RSP: 0018:ffff888105387bf0 EFLAGS: 00010282 > RAX: 0000000000000000 RBX: 0000000490000fff RCX: 0000000000000000 > RDX: 0000000000000001 RSI: 0000000000000003 RDI: ffffed1020a70f73 > RBP: 0000000000000000 R08: ffffed100d9fce92 R09: 0000000000000001 > R10: ffffffff892348e7 R11: ffffed100d9fce91 R12: 0000000490000000 > R13: 0000000000000001 R14: 0000000000000001 R15: ffff888105387ca0 > FS: 00007f86c438c740(0000) GS:ffff88806ce00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 000055ba75b1b818 CR3: 0000000005231000 CR4: 0000000000350eb0 > Call Trace: > <TASK> > ? __warn+0xd7/0x1b8 > ? __ioremap_caller.constprop.0+0x131/0x35d > ? report_bug+0x136/0x19e > ? __ioremap_caller.constprop.0+0x131/0x35d > ? handle_bug+0x3c/0x64 > ? exc_invalid_op+0x13/0x38 > ? asm_exc_invalid_op+0x16/0x20 > ? irq_work_claim+0x16/0x38 > ? __ioremap_caller.constprop.0+0x131/0x35d > ? tracer_hardirqs_off+0x18/0x16d > ? kmem_cache_debug_flags+0x16/0x23 > ? memremap+0xcb/0x184 > ? iounmap+0xfe/0xfe > ? lock_sync+0xc7/0xc7 > ? lock_sync+0xc7/0xc7 > ? rcu_is_watching+0x1c/0x38 > ? do_raw_read_unlock+0x37/0x42 > ? _raw_read_unlock+0x1f/0x2f > memremap+0xcb/0x184 > ? pfn_valid+0x159/0x159 > ? resource_is_exclusive+0xba/0xc5 > xlate_dev_mem_ptr+0x25/0x2f > write_mem+0x94/0xfb > vfs_write+0x128/0x26d > ? kernel_write+0x89/0x89 > ? rcu_is_watching+0x1c/0x38 > ? __might_fault+0x72/0xba > ? __might_fault+0x72/0xba > ? rcu_is_watching+0x1c/0x38 > ? lock_release+0xba/0x13e > ? files_lookup_fd_raw+0x40/0x4b > ? __fget_light+0x64/0x89 > ksys_write+0xac/0xfe > ? __ia32_sys_read+0x40/0x40 > ? tracer_hardirqs_off+0x18/0x16d > ? tracer_hardirqs_on+0x11/0x146 > do_syscall_64+0x9a/0xfd > entry_SYSCALL_64_after_hwframe+0x4b/0x53 > RIP: 0033:0x7f86c4487140 > Code: 40 00 48 8b 15 c1 9c 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 80 3d a1 24 0e 00 00 74 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 48 89 > RSP: 002b:00007ffca9f62af8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 > RAX: ffffffffffffffda RBX: 0000000000000400 RCX: 00007f86c4487140 > RDX: 0000000000000400 RSI: 000055ba75b1a000 RDI: 0000000000000001 > RBP: 000055ba75b1a000 R08: 0000000000000000 R09: 00007f86c457c080 > R10: 00007f86c43a84d0 R11: 0000000000000202 R12: 0000000000000000 > R13: 0000000000000000 R14: 000055ba75b1a000 R15: 0000000000000400 > </TASK> > irq event stamp: 0 > hardirqs last enabled at (0): [<0000000000000000>] 0x0 > hardirqs last disabled at (0): [<ffffffff89091e85>] copy_process+0xb60/0x255f > softirqs last enabled at (0): [<ffffffff89091e85>] copy_process+0xb60/0x255f > softirqs last disabled at (0): [<0000000000000000>] 0x0 > > After investigation, we found the following bug. > > In the above resource tree, "System RAM" is a descendant of "CXL > Window 0" instead of a top level resource. So, region_intersects() > will report no System RAM resources in the CXL memory region > incorrectly, because it only checks the top level resources. > Consequently, devmem_is_allowed() will return 1 (allow access via > /dev/mem) for CXL memory region incorrectly. Fortunately, ioremap() > doesn't allow to map System RAM and reject the access. > > However, region_intersects() needs to be fixed to work correctly with > the resources tree with CXL Window as above. To fix it, we will > search matched resources in the descendant resources too. So, we will > not miss any matched resources anymore. Thanks for this Ying! I think this needs an explanation of the expected semantics of region_intersects() and maybe a fixup to meet that expectation, see below. > Signed-off-by: "Huang, Ying" <ying.huang@intel.com> > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: Davidlohr Bueso <dave@stgolabs.net> > Cc: Jonathan Cameron <jonathan.cameron@huawei.com> > Cc: Dave Jiang <dave.jiang@intel.com> > Cc: Alison Schofield <alison.schofield@intel.com> > Cc: Vishal Verma <vishal.l.verma@intel.com> > Cc: Ira Weiny <ira.weiny@intel.com> > Cc: Alistair Popple <apopple@nvidia.com> > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > Cc: Bjorn Helgaas <bhelgaas@google.com> > Cc: Baoquan He <bhe@redhat.com> > --- > kernel/resource.c | 44 +++++++++++++++++++++++++++++++++++++------- > 1 file changed, 37 insertions(+), 7 deletions(-) > > diff --git a/kernel/resource.c b/kernel/resource.c > index 14777afb0a99..c97a5add9394 100644 > --- a/kernel/resource.c > +++ b/kernel/resource.c > @@ -542,18 +542,48 @@ static int __region_intersects(struct resource *parent, resource_size_t start, > { > struct resource res; > int type = 0; int other = 0; > - struct resource *p; > + struct resource *p, *dp; > + resource_size_t ostart, oend; > + bool is_type; > > res.start = start; > res.end = start + size - 1; > > for (p = parent->child; p ; p = p->sibling) { > - bool is_type = (((p->flags & flags) == flags) && > - ((desc == IORES_DESC_NONE) || > - (desc == p->desc))); > - > - if (resource_overlaps(p, &res)) > - is_type ? type++ : other++; > + if (!resource_overlaps(p, &res)) > + continue; > + is_type = (((p->flags & flags) == flags) && > + ((desc == IORES_DESC_NONE) || (desc == p->desc))); > + if (is_type) { > + type++; > + continue; > + } > + /* > + * Continue to search in descendant resources. Unless > + * the matched descendant resources cover the whole > + * overlapped range, increase 'other', because it > + * overlaps with 'p' at least. > + */ > + other++; This results in REGION_MIXED whenever the target of the search is found as a descendant of @parent which I believe is unwanted. The semantics of region_intersects() has always been within a single sibling level to date. So, I don't think @other should be incremented until @is_type is non-zero. It follows that if @is_type is set and !resource_contains(p, &res) then there is no point in descending because it is known at that there are no descendants to worry about. I do note that with those changes region_intersects() will start reporting REGION_MIXED rather than REGION_INTERSECTS when the passed in range intersects a hole plus the target, but I am not aware of any code path that expects to ignore resource holes. I.e. better to report holes as occupied in that case. Lastly, it would probably also be useful to special case the "@flags == 0 && @desc == IORES_DESC_NONE" case because there is no point in descending the resource tree to look for additional holes. Those are all visible at the top of the resource tree.
[ add David ] Andrew Morton wrote: > On Fri, 16 Aug 2024 10:07:23 +0800 Huang Ying <ying.huang@intel.com> wrote: > > > On a system with CXL memory installed, the resource tree (/proc/iomem) > > related to CXL memory looks like something as follows. > > > > 490000000-50fffffff : CXL Window 0 > > 490000000-50fffffff : region0 > > 490000000-50fffffff : dax0.0 > > 490000000-50fffffff : System RAM (kmem) > > > > When the following command line is run to try writing some memory in > > CXL memory range, > > > > $ dd if=data of=/dev/mem bs=1k seek=19136512 count=1 > > dd: error writing '/dev/mem': Bad address > > 1+0 records in > > 0+0 records out > > 0 bytes copied, 0.0283507 s, 0.0 kB/s > > > > the command fails as expected. However, the error code is wrong. It > > should be "Operation not permitted" instead of "Bad address". And, > > the following warning is reported in kernel log. > > > > ioremap on RAM at 0x0000000490000000 - 0x0000000490000fff > > WARNING: CPU: 2 PID: 416 at arch/x86/mm/ioremap.c:216 __ioremap_caller.constprop.0+0x131/0x35d > > ... > > > > Presumably we want to fix earlier kernels? If so, are you able to > identify a suitable Fixes: target? Possibly 974854ab0728 ("cxl/acpi: > Track CXL resources in iomem_resource")? At least that commit, but I think this problem potentially goes back farther to: c221c0b0308f device-dax: "Hotplug" persistent memory for use like normal RAM ...because that started the era of "System RAM" as a non-top-level resource. David did a bunch of work to fix this back in: 97f61c8f44ec kernel/resource: make walk_system_ram_res() find all busy IORESOURCE_SYSTEM_RAM resources ..but the fallout in region_intersects() was missed.
Dan Williams <dan.j.williams@intel.com> writes: > Huang Ying wrote: >> On a system with CXL memory installed, the resource tree (/proc/iomem) >> related to CXL memory looks like something as follows. >> >> 490000000-50fffffff : CXL Window 0 >> 490000000-50fffffff : region0 >> 490000000-50fffffff : dax0.0 >> 490000000-50fffffff : System RAM (kmem) >> >> When the following command line is run to try writing some memory in >> CXL memory range, >> >> $ dd if=data of=/dev/mem bs=1k seek=19136512 count=1 >> dd: error writing '/dev/mem': Bad address >> 1+0 records in >> 0+0 records out >> 0 bytes copied, 0.0283507 s, 0.0 kB/s >> >> the command fails as expected. However, the error code is wrong. It >> should be "Operation not permitted" instead of "Bad address". And, >> the following warning is reported in kernel log. >> >> ioremap on RAM at 0x0000000490000000 - 0x0000000490000fff >> WARNING: CPU: 2 PID: 416 at arch/x86/mm/ioremap.c:216 __ioremap_caller.constprop.0+0x131/0x35d >> Modules linked in: cxl_pmem libnvdimm cbc encrypted_keys cxl_pmu >> CPU: 2 UID: 0 PID: 416 Comm: dd Not tainted 6.11.0-rc3-kvm #40 >> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 >> RIP: 0010:__ioremap_caller.constprop.0+0x131/0x35d >> Code: 2d 80 3d 24 6a a1 02 00 75 c1 48 8d 54 24 70 48 8d b4 24 90 00 00 00 48 c7 c7 40 3a 05 8a c6 05 07 6a a1 02 01 e8 a3 a0 01 00 <0f> 0b eb 9d 48 8b 84 24 90 00 00 00 48 8d 4c 24 60 89 ea 48 bf 00 >> RSP: 0018:ffff888105387bf0 EFLAGS: 00010282 >> RAX: 0000000000000000 RBX: 0000000490000fff RCX: 0000000000000000 >> RDX: 0000000000000001 RSI: 0000000000000003 RDI: ffffed1020a70f73 >> RBP: 0000000000000000 R08: ffffed100d9fce92 R09: 0000000000000001 >> R10: ffffffff892348e7 R11: ffffed100d9fce91 R12: 0000000490000000 >> R13: 0000000000000001 R14: 0000000000000001 R15: ffff888105387ca0 >> FS: 00007f86c438c740(0000) GS:ffff88806ce00000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 000055ba75b1b818 CR3: 0000000005231000 CR4: 0000000000350eb0 >> Call Trace: >> <TASK> >> ? __warn+0xd7/0x1b8 >> ? __ioremap_caller.constprop.0+0x131/0x35d >> ? report_bug+0x136/0x19e >> ? __ioremap_caller.constprop.0+0x131/0x35d >> ? handle_bug+0x3c/0x64 >> ? exc_invalid_op+0x13/0x38 >> ? asm_exc_invalid_op+0x16/0x20 >> ? irq_work_claim+0x16/0x38 >> ? __ioremap_caller.constprop.0+0x131/0x35d >> ? tracer_hardirqs_off+0x18/0x16d >> ? kmem_cache_debug_flags+0x16/0x23 >> ? memremap+0xcb/0x184 >> ? iounmap+0xfe/0xfe >> ? lock_sync+0xc7/0xc7 >> ? lock_sync+0xc7/0xc7 >> ? rcu_is_watching+0x1c/0x38 >> ? do_raw_read_unlock+0x37/0x42 >> ? _raw_read_unlock+0x1f/0x2f >> memremap+0xcb/0x184 >> ? pfn_valid+0x159/0x159 >> ? resource_is_exclusive+0xba/0xc5 >> xlate_dev_mem_ptr+0x25/0x2f >> write_mem+0x94/0xfb >> vfs_write+0x128/0x26d >> ? kernel_write+0x89/0x89 >> ? rcu_is_watching+0x1c/0x38 >> ? __might_fault+0x72/0xba >> ? __might_fault+0x72/0xba >> ? rcu_is_watching+0x1c/0x38 >> ? lock_release+0xba/0x13e >> ? files_lookup_fd_raw+0x40/0x4b >> ? __fget_light+0x64/0x89 >> ksys_write+0xac/0xfe >> ? __ia32_sys_read+0x40/0x40 >> ? tracer_hardirqs_off+0x18/0x16d >> ? tracer_hardirqs_on+0x11/0x146 >> do_syscall_64+0x9a/0xfd >> entry_SYSCALL_64_after_hwframe+0x4b/0x53 >> RIP: 0033:0x7f86c4487140 >> Code: 40 00 48 8b 15 c1 9c 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 80 3d a1 24 0e 00 00 74 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 48 89 >> RSP: 002b:00007ffca9f62af8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 >> RAX: ffffffffffffffda RBX: 0000000000000400 RCX: 00007f86c4487140 >> RDX: 0000000000000400 RSI: 000055ba75b1a000 RDI: 0000000000000001 >> RBP: 000055ba75b1a000 R08: 0000000000000000 R09: 00007f86c457c080 >> R10: 00007f86c43a84d0 R11: 0000000000000202 R12: 0000000000000000 >> R13: 0000000000000000 R14: 000055ba75b1a000 R15: 0000000000000400 >> </TASK> >> irq event stamp: 0 >> hardirqs last enabled at (0): [<0000000000000000>] 0x0 >> hardirqs last disabled at (0): [<ffffffff89091e85>] copy_process+0xb60/0x255f >> softirqs last enabled at (0): [<ffffffff89091e85>] copy_process+0xb60/0x255f >> softirqs last disabled at (0): [<0000000000000000>] 0x0 >> >> After investigation, we found the following bug. >> >> In the above resource tree, "System RAM" is a descendant of "CXL >> Window 0" instead of a top level resource. So, region_intersects() >> will report no System RAM resources in the CXL memory region >> incorrectly, because it only checks the top level resources. >> Consequently, devmem_is_allowed() will return 1 (allow access via >> /dev/mem) for CXL memory region incorrectly. Fortunately, ioremap() >> doesn't allow to map System RAM and reject the access. >> >> However, region_intersects() needs to be fixed to work correctly with >> the resources tree with CXL Window as above. To fix it, we will >> search matched resources in the descendant resources too. So, we will >> not miss any matched resources anymore. > > Thanks for this Ying! > > I think this needs an explanation of the expected semantics of > region_intersects() and maybe a fixup to meet that expectation, see > below. > >> Signed-off-by: "Huang, Ying" <ying.huang@intel.com> >> Cc: Dan Williams <dan.j.williams@intel.com> >> Cc: Davidlohr Bueso <dave@stgolabs.net> >> Cc: Jonathan Cameron <jonathan.cameron@huawei.com> >> Cc: Dave Jiang <dave.jiang@intel.com> >> Cc: Alison Schofield <alison.schofield@intel.com> >> Cc: Vishal Verma <vishal.l.verma@intel.com> >> Cc: Ira Weiny <ira.weiny@intel.com> >> Cc: Alistair Popple <apopple@nvidia.com> >> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> >> Cc: Bjorn Helgaas <bhelgaas@google.com> >> Cc: Baoquan He <bhe@redhat.com> >> --- >> kernel/resource.c | 44 +++++++++++++++++++++++++++++++++++++------- >> 1 file changed, 37 insertions(+), 7 deletions(-) >> >> diff --git a/kernel/resource.c b/kernel/resource.c >> index 14777afb0a99..c97a5add9394 100644 >> --- a/kernel/resource.c >> +++ b/kernel/resource.c >> @@ -542,18 +542,48 @@ static int __region_intersects(struct resource *parent, resource_size_t start, >> { >> struct resource res; >> int type = 0; int other = 0; >> - struct resource *p; >> + struct resource *p, *dp; >> + resource_size_t ostart, oend; >> + bool is_type; >> >> res.start = start; >> res.end = start + size - 1; >> >> for (p = parent->child; p ; p = p->sibling) { >> - bool is_type = (((p->flags & flags) == flags) && >> - ((desc == IORES_DESC_NONE) || >> - (desc == p->desc))); >> - >> - if (resource_overlaps(p, &res)) >> - is_type ? type++ : other++; >> + if (!resource_overlaps(p, &res)) >> + continue; >> + is_type = (((p->flags & flags) == flags) && >> + ((desc == IORES_DESC_NONE) || (desc == p->desc))); >> + if (is_type) { >> + type++; >> + continue; >> + } >> + /* >> + * Continue to search in descendant resources. Unless >> + * the matched descendant resources cover the whole >> + * overlapped range, increase 'other', because it >> + * overlaps with 'p' at least. >> + */ >> + other++; > > This results in REGION_MIXED whenever the target of the search is found > as a descendant of @parent which I believe is unwanted. This is not the behavior of this patch. There's a "other--" later in this patch. + ostart = max(res.start, p->start); + oend = min(res.end, p->end); + for_each_resource(p, dp, false) { + if (!resource_overlaps(dp, &res)) + continue; + is_type = (((dp->flags & flags) == flags) && + ((desc == IORES_DESC_NONE) || + (desc == dp->desc))); + if (is_type) { + type++; + if (dp->start > ostart) + break; + if (dp->end >= oend) { + other--; <====================== HERE! + break; + } + ostart = dp->end + 1; + } + } } if (type == 0) That is, if the overlapped range is covered by matched (is_type == true) descendant resources completely, other will not increase. So, for resource tree as follows 490000000-52fffffff : CXL Window 0 490000000-50fffffff : region0 490000000-50fffffff : dax0.0 490000000-50fffffff : System RAM (kmem) 510000000-52fffffff 510000000-52fffffff : dax0.1 region_intersects(, 0x490000000, PAGE_SIZE, IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE) => REGION_INTERSECTS region_intersects(, 0x50f000000, 0x2000000, IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE) => REGION_MIXED Even for 490000000-52fffffff : CXL Window 0 490000000-50fffffff : region0 490000000-50fffffff : dax0.0 490000000-50fffffff : System RAM (kmem) region_intersects(, 0x50f000000, 0x2000000, IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE) => REGION_MIXED This isn't perfect, but it looks OK for me. Because for 490000000-50fffffff : System RAM 510000000-52fffffff : CXL Window 0 region_intersects(, 0x50f000000, 0x2000000, IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE) => REGION_MIXED However, I admit that the original code is hard to be understood, whether is something like below better? for (p = parent->child; p ; p = p->sibling) { if (!resource_overlaps(p, &res)) continue; is_type = (((p->flags & flags) == flags) && ((desc == IORES_DESC_NONE) || (desc == p->desc))); if (is_type) { type++; continue; } /* * Continue to search in descendant resources. Unless * the matched descendant resources cover the whole * overlapped range, increase 'other', because it * overlaps with 'p' at least. */ covered = false; ostart = max(res.start, p->start); oend = min(res.end, p->end); for_each_resource(p, dp, false) { if (!resource_overlaps(dp, &res)) continue; is_type = (((dp->flags & flags) == flags) && ((desc == IORES_DESC_NONE) || (desc == dp->desc))); if (is_type) { type++; if (dp->start > ostart) break; if (dp->end >= oend) { covered = true; break; } ostart = dp->end + 1; } } if (!covered) other++; } > The semantics of region_intersects() has always been within a single > sibling level to date. So, I don't think @other should be incremented > until @is_type is non-zero. It follows that if @is_type is set and > !resource_contains(p, &res) then there is no point in descending because > it is known at that there are no descendants to worry about. Sorry, I don't understand your words here. Can you show your idea with some examples or pseudo code? > I do note that with those changes region_intersects() will start > reporting REGION_MIXED rather than REGION_INTERSECTS when the passed in > range intersects a hole plus the target, but I am not aware of any code > path that expects to ignore resource holes. I.e. better to report holes > as occupied in that case. > > Lastly, it would probably also be useful to special case the "@flags == > 0 && @desc == IORES_DESC_NONE" case because there is no point in > descending the resource tree to look for additional holes. Those are all > visible at the top of the resource tree. -- Best Regards, Huang, Ying
On 16.08.24 07:07, Dan Williams wrote: > [ add David ] > > Andrew Morton wrote: >> On Fri, 16 Aug 2024 10:07:23 +0800 Huang Ying <ying.huang@intel.com> wrote: >> >>> On a system with CXL memory installed, the resource tree (/proc/iomem) >>> related to CXL memory looks like something as follows. >>> >>> 490000000-50fffffff : CXL Window 0 >>> 490000000-50fffffff : region0 >>> 490000000-50fffffff : dax0.0 >>> 490000000-50fffffff : System RAM (kmem) >>> >>> When the following command line is run to try writing some memory in >>> CXL memory range, >>> >>> $ dd if=data of=/dev/mem bs=1k seek=19136512 count=1 >>> dd: error writing '/dev/mem': Bad address >>> 1+0 records in >>> 0+0 records out >>> 0 bytes copied, 0.0283507 s, 0.0 kB/s >>> >>> the command fails as expected. However, the error code is wrong. It >>> should be "Operation not permitted" instead of "Bad address". And, >>> the following warning is reported in kernel log. >>> >>> ioremap on RAM at 0x0000000490000000 - 0x0000000490000fff >>> WARNING: CPU: 2 PID: 416 at arch/x86/mm/ioremap.c:216 __ioremap_caller.constprop.0+0x131/0x35d But we should definitely fix the warning. >>> ... >>> >> >> Presumably we want to fix earlier kernels? If so, are you able to >> identify a suitable Fixes: target? Possibly 974854ab0728 ("cxl/acpi: >> Track CXL resources in iomem_resource")? > > At least that commit, but I think this problem potentially goes back > farther to: > > c221c0b0308f device-dax: "Hotplug" persistent memory for use like normal RAM > > ...because that started the era of "System RAM" as a non-top-level > resource. > > David did a bunch of work to fix this back in: > > 97f61c8f44ec kernel/resource: make walk_system_ram_res() find all busy IORESOURCE_SYSTEM_RAM resources > > ..but the fallout in region_intersects() was missed. Sounds reasonable. For virtio-mem we set IORESOURCE_SYSTEM_RAM|IORESOURCE_EXCLUSIVE on our (highest) parent resource (to make any /dev/mem access attempts of that memory fail). So the problem is likely specific to other add_memory_driver_managed() users. I have a faint recollection that at some point we had code that would set IORESOURCE_SYSTEM_RAM on parent resources up the tree, but either my memory is wrong or that code was ripped out long ago. Fix idea is reasonable: check if anything in that range is IORESOURCE_SYSTEM_RAM.
Huang, Ying wrote: > Dan Williams <dan.j.williams@intel.com> writes: > > Huang Ying wrote: [..] > >> kernel/resource.c | 44 +++++++++++++++++++++++++++++++++++++------- > >> 1 file changed, 37 insertions(+), 7 deletions(-) > >> > >> diff --git a/kernel/resource.c b/kernel/resource.c > >> index 14777afb0a99..c97a5add9394 100644 > >> --- a/kernel/resource.c > >> +++ b/kernel/resource.c [..] > >> + /* > >> + * Continue to search in descendant resources. Unless > >> + * the matched descendant resources cover the whole > >> + * overlapped range, increase 'other', because it > >> + * overlaps with 'p' at least. > >> + */ > >> + other++; > > > > This results in REGION_MIXED whenever the target of the search is found > > as a descendant of @parent which I believe is unwanted. > > This is not the behavior of this patch. There's a "other--" later in > this patch. > > + ostart = max(res.start, p->start); > + oend = min(res.end, p->end); > + for_each_resource(p, dp, false) { > + if (!resource_overlaps(dp, &res)) > + continue; > + is_type = (((dp->flags & flags) == flags) && > + ((desc == IORES_DESC_NONE) || > + (desc == dp->desc))); > + if (is_type) { > + type++; > + if (dp->start > ostart) > + break; > + if (dp->end >= oend) { > + other--; <====================== HERE! Yes, I missed that. > + break; > + } > + ostart = dp->end + 1; > + } > + } > } > > if (type == 0) > > > That is, if the overlapped range is covered by matched (is_type == true) > descendant resources completely, other will not increase. > > So, for resource tree as follows > > 490000000-52fffffff : CXL Window 0 > 490000000-50fffffff : region0 > 490000000-50fffffff : dax0.0 > 490000000-50fffffff : System RAM (kmem) > 510000000-52fffffff > 510000000-52fffffff : dax0.1 > > region_intersects(, 0x490000000, PAGE_SIZE, IORESOURCE_SYSTEM_RAM, > IORES_DESC_NONE) => REGION_INTERSECTS > region_intersects(, 0x50f000000, 0x2000000, IORESOURCE_SYSTEM_RAM, > IORES_DESC_NONE) => REGION_MIXED > > Even for > > 490000000-52fffffff : CXL Window 0 > 490000000-50fffffff : region0 > 490000000-50fffffff : dax0.0 > 490000000-50fffffff : System RAM (kmem) > > region_intersects(, 0x50f000000, 0x2000000, IORESOURCE_SYSTEM_RAM, > IORES_DESC_NONE) => REGION_MIXED > > This isn't perfect, but it looks OK for me. Because for > > 490000000-50fffffff : System RAM > 510000000-52fffffff : CXL Window 0 > > region_intersects(, 0x50f000000, 0x2000000, IORESOURCE_SYSTEM_RAM, > IORES_DESC_NONE) => REGION_MIXED That explanation makes sense and matches my expectation. > However, I admit that the original code is hard to be understood, > whether is something like below better? I like that this proposal defers incrementing @other rather than decrement after the fact. > > for (p = parent->child; p ; p = p->sibling) { > if (!resource_overlaps(p, &res)) > continue; > is_type = (((p->flags & flags) == flags) && > ((desc == IORES_DESC_NONE) || (desc == p->desc))); > if (is_type) { > type++; > continue; > } > /* > * Continue to search in descendant resources. Unless > * the matched descendant resources cover the whole > * overlapped range, increase 'other', because it > * overlaps with 'p' at least. > */ > covered = false; I would call @covered, @single_descendant. Since @covered is ambiguous. > ostart = max(res.start, p->start); > oend = min(res.end, p->end); > for_each_resource(p, dp, false) { > if (!resource_overlaps(dp, &res)) > continue; > is_type = (((dp->flags & flags) == flags) && > ((desc == IORES_DESC_NONE) || > (desc == dp->desc))); > if (is_type) { > type++; > if (dp->start > ostart) ...this should have a comment: /* partial descendant overlap indicates overlap with a descendant hole */ > break; > if (dp->end >= oend) { > covered = true; > break; ...then per above this because easier to read as: single_descendant = true; > } > ostart = dp->end + 1; > } > } > if (!covered) > other++; > } > > > The semantics of region_intersects() has always been within a single > > sibling level to date. So, I don't think @other should be incremented > > until @is_type is non-zero. It follows that if @is_type is set and > > !resource_contains(p, &res) then there is no point in descending because > > it is known at that there are no descendants to worry about. > > Sorry, I don't understand your words here. Can you show your idea with > some examples or pseudo code? I think your proposed updates address my concern.
Dan Williams <dan.j.williams@intel.com> writes: > Huang, Ying wrote: >> Dan Williams <dan.j.williams@intel.com> writes: >> > Huang Ying wrote: > [..] >> >> kernel/resource.c | 44 +++++++++++++++++++++++++++++++++++++------- >> >> 1 file changed, 37 insertions(+), 7 deletions(-) >> >> >> >> diff --git a/kernel/resource.c b/kernel/resource.c >> >> index 14777afb0a99..c97a5add9394 100644 >> >> --- a/kernel/resource.c >> >> +++ b/kernel/resource.c > [..] [snip] > >> However, I admit that the original code is hard to be understood, >> whether is something like below better? > > I like that this proposal defers incrementing @other rather than > decrement after the fact. > >> >> for (p = parent->child; p ; p = p->sibling) { >> if (!resource_overlaps(p, &res)) >> continue; >> is_type = (((p->flags & flags) == flags) && >> ((desc == IORES_DESC_NONE) || (desc == p->desc))); >> if (is_type) { >> type++; >> continue; >> } >> /* >> * Continue to search in descendant resources. Unless >> * the matched descendant resources cover the whole >> * overlapped range, increase 'other', because it >> * overlaps with 'p' at least. >> */ >> covered = false; > > I would call @covered, @single_descendant. Since @covered is ambiguous. Sorry, I don't understand why this is called @single_descendant. It's possible that the checked region is overlapped with 2 descendants, and the result is REGION_INTERSECTS. For example, 490000000-52fffffff : CXL Window 0 490000000-50fffffff : region0 490000000-50fffffff : dax0.0 490000000-50fffffff : System RAM (kmem) 510000000-52fffffff : region1 510000000-52fffffff : dax0.1 510000000-52fffffff : System RAM (kmem) region_intersects(, 0x50ffff000, 2 * PAGE_SIZE, IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE) => REGION_INTERSECTS >> ostart = max(res.start, p->start); >> oend = min(res.end, p->end); >> for_each_resource(p, dp, false) { >> if (!resource_overlaps(dp, &res)) >> continue; >> is_type = (((dp->flags & flags) == flags) && >> ((desc == IORES_DESC_NONE) || >> (desc == dp->desc))); >> if (is_type) { >> type++; >> if (dp->start > ostart) > > ...this should have a comment: > > /* partial descendant overlap indicates overlap with a descendant hole */ Yes. Some comments should help. >> break; >> if (dp->end >= oend) { >> covered = true; >> break; > > ...then per above this because easier to read as: > > single_descendant = true; > >> } >> ostart = dp->end + 1; >> } >> } >> if (!covered) >> other++; >> } >> [snip] -- Best Regards, Huang, Ying
On Mon, Sep 02, 2024 at 10:07:52AM +0800, Huang, Ying wrote: > Dan Williams <dan.j.williams@intel.com> writes: > > Huang, Ying wrote: > >> Dan Williams <dan.j.williams@intel.com> writes: > >> > Huang Ying wrote: [..] Looking at how many troubles touching kernel/resource.c may lead to, here is the question(s): 1) do we have a test cases in general for this library? 2) can this change be coupled with an addition/update of the test cases?
Hi, Andy, Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes: > On Mon, Sep 02, 2024 at 10:07:52AM +0800, Huang, Ying wrote: >> Dan Williams <dan.j.williams@intel.com> writes: >> > Huang, Ying wrote: >> >> Dan Williams <dan.j.williams@intel.com> writes: >> >> > Huang Ying wrote: > > [..] > > Looking at how many troubles touching kernel/resource.c may lead to, here is > the question(s): > 1) do we have a test cases in general for this library? > 2) can this change be coupled with an addition/update of the test cases? Yes. This is reasonable. As far as I know, Dan has plan to add some unit tests for region_intersects(). Hi, Dan, Have you started working on the unit tests? If needed, please let me know so I can assist. -- Best Regards, Huang, Ying
diff --git a/kernel/resource.c b/kernel/resource.c index 14777afb0a99..c97a5add9394 100644 --- a/kernel/resource.c +++ b/kernel/resource.c @@ -542,18 +542,48 @@ static int __region_intersects(struct resource *parent, resource_size_t start, { struct resource res; int type = 0; int other = 0; - struct resource *p; + struct resource *p, *dp; + resource_size_t ostart, oend; + bool is_type; res.start = start; res.end = start + size - 1; for (p = parent->child; p ; p = p->sibling) { - bool is_type = (((p->flags & flags) == flags) && - ((desc == IORES_DESC_NONE) || - (desc == p->desc))); - - if (resource_overlaps(p, &res)) - is_type ? type++ : other++; + if (!resource_overlaps(p, &res)) + continue; + is_type = (((p->flags & flags) == flags) && + ((desc == IORES_DESC_NONE) || (desc == p->desc))); + if (is_type) { + type++; + continue; + } + /* + * Continue to search in descendant resources. Unless + * the matched descendant resources cover the whole + * overlapped range, increase 'other', because it + * overlaps with 'p' at least. + */ + other++; + ostart = max(res.start, p->start); + oend = min(res.end, p->end); + for_each_resource(p, dp, false) { + if (!resource_overlaps(dp, &res)) + continue; + is_type = (((dp->flags & flags) == flags) && + ((desc == IORES_DESC_NONE) || + (desc == dp->desc))); + if (is_type) { + type++; + if (dp->start > ostart) + break; + if (dp->end >= oend) { + other--; + break; + } + ostart = dp->end + 1; + } + } } if (type == 0)
On a system with CXL memory installed, the resource tree (/proc/iomem) related to CXL memory looks like something as follows. 490000000-50fffffff : CXL Window 0 490000000-50fffffff : region0 490000000-50fffffff : dax0.0 490000000-50fffffff : System RAM (kmem) When the following command line is run to try writing some memory in CXL memory range, $ dd if=data of=/dev/mem bs=1k seek=19136512 count=1 dd: error writing '/dev/mem': Bad address 1+0 records in 0+0 records out 0 bytes copied, 0.0283507 s, 0.0 kB/s the command fails as expected. However, the error code is wrong. It should be "Operation not permitted" instead of "Bad address". And, the following warning is reported in kernel log. ioremap on RAM at 0x0000000490000000 - 0x0000000490000fff WARNING: CPU: 2 PID: 416 at arch/x86/mm/ioremap.c:216 __ioremap_caller.constprop.0+0x131/0x35d Modules linked in: cxl_pmem libnvdimm cbc encrypted_keys cxl_pmu CPU: 2 UID: 0 PID: 416 Comm: dd Not tainted 6.11.0-rc3-kvm #40 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 RIP: 0010:__ioremap_caller.constprop.0+0x131/0x35d Code: 2d 80 3d 24 6a a1 02 00 75 c1 48 8d 54 24 70 48 8d b4 24 90 00 00 00 48 c7 c7 40 3a 05 8a c6 05 07 6a a1 02 01 e8 a3 a0 01 00 <0f> 0b eb 9d 48 8b 84 24 90 00 00 00 48 8d 4c 24 60 89 ea 48 bf 00 RSP: 0018:ffff888105387bf0 EFLAGS: 00010282 RAX: 0000000000000000 RBX: 0000000490000fff RCX: 0000000000000000 RDX: 0000000000000001 RSI: 0000000000000003 RDI: ffffed1020a70f73 RBP: 0000000000000000 R08: ffffed100d9fce92 R09: 0000000000000001 R10: ffffffff892348e7 R11: ffffed100d9fce91 R12: 0000000490000000 R13: 0000000000000001 R14: 0000000000000001 R15: ffff888105387ca0 FS: 00007f86c438c740(0000) GS:ffff88806ce00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055ba75b1b818 CR3: 0000000005231000 CR4: 0000000000350eb0 Call Trace: <TASK> ? __warn+0xd7/0x1b8 ? __ioremap_caller.constprop.0+0x131/0x35d ? report_bug+0x136/0x19e ? __ioremap_caller.constprop.0+0x131/0x35d ? handle_bug+0x3c/0x64 ? exc_invalid_op+0x13/0x38 ? asm_exc_invalid_op+0x16/0x20 ? irq_work_claim+0x16/0x38 ? __ioremap_caller.constprop.0+0x131/0x35d ? tracer_hardirqs_off+0x18/0x16d ? kmem_cache_debug_flags+0x16/0x23 ? memremap+0xcb/0x184 ? iounmap+0xfe/0xfe ? lock_sync+0xc7/0xc7 ? lock_sync+0xc7/0xc7 ? rcu_is_watching+0x1c/0x38 ? do_raw_read_unlock+0x37/0x42 ? _raw_read_unlock+0x1f/0x2f memremap+0xcb/0x184 ? pfn_valid+0x159/0x159 ? resource_is_exclusive+0xba/0xc5 xlate_dev_mem_ptr+0x25/0x2f write_mem+0x94/0xfb vfs_write+0x128/0x26d ? kernel_write+0x89/0x89 ? rcu_is_watching+0x1c/0x38 ? __might_fault+0x72/0xba ? __might_fault+0x72/0xba ? rcu_is_watching+0x1c/0x38 ? lock_release+0xba/0x13e ? files_lookup_fd_raw+0x40/0x4b ? __fget_light+0x64/0x89 ksys_write+0xac/0xfe ? __ia32_sys_read+0x40/0x40 ? tracer_hardirqs_off+0x18/0x16d ? tracer_hardirqs_on+0x11/0x146 do_syscall_64+0x9a/0xfd entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f86c4487140 Code: 40 00 48 8b 15 c1 9c 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 80 3d a1 24 0e 00 00 74 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 48 89 RSP: 002b:00007ffca9f62af8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 0000000000000400 RCX: 00007f86c4487140 RDX: 0000000000000400 RSI: 000055ba75b1a000 RDI: 0000000000000001 RBP: 000055ba75b1a000 R08: 0000000000000000 R09: 00007f86c457c080 R10: 00007f86c43a84d0 R11: 0000000000000202 R12: 0000000000000000 R13: 0000000000000000 R14: 000055ba75b1a000 R15: 0000000000000400 </TASK> irq event stamp: 0 hardirqs last enabled at (0): [<0000000000000000>] 0x0 hardirqs last disabled at (0): [<ffffffff89091e85>] copy_process+0xb60/0x255f softirqs last enabled at (0): [<ffffffff89091e85>] copy_process+0xb60/0x255f softirqs last disabled at (0): [<0000000000000000>] 0x0 After investigation, we found the following bug. In the above resource tree, "System RAM" is a descendant of "CXL Window 0" instead of a top level resource. So, region_intersects() will report no System RAM resources in the CXL memory region incorrectly, because it only checks the top level resources. Consequently, devmem_is_allowed() will return 1 (allow access via /dev/mem) for CXL memory region incorrectly. Fortunately, ioremap() doesn't allow to map System RAM and reject the access. However, region_intersects() needs to be fixed to work correctly with the resources tree with CXL Window as above. To fix it, we will search matched resources in the descendant resources too. So, we will not miss any matched resources anymore. Signed-off-by: "Huang, Ying" <ying.huang@intel.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Jonathan Cameron <jonathan.cameron@huawei.com> Cc: Dave Jiang <dave.jiang@intel.com> Cc: Alison Schofield <alison.schofield@intel.com> Cc: Vishal Verma <vishal.l.verma@intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Baoquan He <bhe@redhat.com> --- kernel/resource.c | 44 +++++++++++++++++++++++++++++++++++++------- 1 file changed, 37 insertions(+), 7 deletions(-)