| Message ID | 1536024582-25700-5-git-send-email-brijesh.singh@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | x86: Fix SEV guest regression | expand |
On Mon, Sep 03, 2018 at 08:29:42PM -0500, Brijesh Singh wrote: > Commit: 368a540e0232 (x86/kvmclock: Remove memblock dependency) > caused SEV guest regression. When SEV is active, we map the shared > variables (wall_clock and hv_clock_boot) with C=0 to ensure that both > the guest and the hypervisor are able to access the data. To map the > variables we use kernel_physical_mapping_init() to split the large pages, > but splitting large pages requires allocating a new PMD, which fails now > that kvmclock initialization is called early during boot. > > Recently we added a special .data..decrypted section to hold the shared > variables. This section is mapped with C=0 early during boot. Use > __decrypted attribute to put the wall_clock and hv_clock_boot in > .data..decrypted section so that they are mapped with C=0. > > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com> > Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> > Fixes: 368a540e0232 ("x86/kvmclock: Remove memblock dependency") > Cc: Tom Lendacky <thomas.lendacky@amd.com> > Cc: kvm@vger.kernel.org > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Borislav Petkov <bp@suse.de> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: linux-kernel@vger.kernel.org > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Sean Christopherson <sean.j.christopherson@intel.com> > Cc: kvm@vger.kernel.org > Cc: "Radim Krčmář" <rkrcmar@redhat.com> > --- > arch/x86/kernel/kvmclock.c | 30 +++++++++++++++++++++++++----- > 1 file changed, 25 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c > index 1e67646..08f5f8a 100644 > --- a/arch/x86/kernel/kvmclock.c > +++ b/arch/x86/kernel/kvmclock.c > @@ -28,6 +28,7 @@ > #include <linux/sched/clock.h> > #include <linux/mm.h> > #include <linux/slab.h> > +#include <linux/set_memory.h> > > #include <asm/hypervisor.h> > #include <asm/mem_encrypt.h> > @@ -61,8 +62,8 @@ early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall); > (PAGE_SIZE / sizeof(struct pvclock_vsyscall_time_info)) > > static struct pvclock_vsyscall_time_info > - hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __aligned(PAGE_SIZE); > -static struct pvclock_wall_clock wall_clock; > + hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __decrypted __aligned(PAGE_SIZE); > +static struct pvclock_wall_clock wall_clock __decrypted; > static DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu); > > static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void) > @@ -267,10 +268,29 @@ static int kvmclock_setup_percpu(unsigned int cpu) > return 0; > > /* Use the static page for the first CPUs, allocate otherwise */ > - if (cpu < HVC_BOOT_ARRAY_SIZE) > + if (cpu < HVC_BOOT_ARRAY_SIZE) { > p = &hv_clock_boot[cpu]; > - else > - p = kzalloc(sizeof(*p), GFP_KERNEL); > + } else { > + int rc; > + unsigned int sz = sizeof(*p); > + > + if (sev_active()) > + sz = PAGE_ALIGN(sz); Hmm, again we're wasting a fairly sizable amount of memory since each CPU is doing a separate 4k allocation. What if we defined an auxilary array in __decrypted to be used for cpus > HVC_BOOT_ARRAY_SIZE when SEV is active? struct pvclock_vsyscall_time_info is 32 bytes so we could handle the max of 8192 CPUs with 256kb of data (252kb if you subtract the pre-existing 4k page), i.e. the SEV case wouldn't need additional memory beyond the 2mb page that's reserved for __decrypted. The non-SEV case could do free_kernel_image_pages() on the unused array (which would need to be page sized) so it wouldn't waste memory. > + > + p = kzalloc(sz, GFP_KERNEL); > + > + /* > + * The physical address of per-cpu variable will be shared with > + * the hypervisor. Let's clear the C-bit before we assign the > + * memory to per_cpu variable. > + */ > + if (p && sev_active()) { > + rc = set_memory_decrypted((unsigned long)p, sz >> PAGE_SHIFT); > + if (rc) @p is being leaked if set_memory_decrypted() fails. > + return rc; > + memset(p, 0, sz); > + } > + } > > per_cpu(hv_clock_per_cpu, cpu) = p; > return p ? 0 : -ENOMEM; > -- > 2.7.4 >
Hi Sean, On 09/04/2018 05:32 PM, Sean Christopherson wrote: ... >> >> /* Use the static page for the first CPUs, allocate otherwise */ >> - if (cpu < HVC_BOOT_ARRAY_SIZE) >> + if (cpu < HVC_BOOT_ARRAY_SIZE) { >> p = &hv_clock_boot[cpu]; >> - else >> - p = kzalloc(sizeof(*p), GFP_KERNEL); >> + } else { >> + int rc; >> + unsigned int sz = sizeof(*p); >> + >> + if (sev_active()) >> + sz = PAGE_ALIGN(sz); > > Hmm, again we're wasting a fairly sizable amount of memory since each > CPU is doing a separate 4k allocation. What if we defined an auxilary > array in __decrypted to be used for cpus > HVC_BOOT_ARRAY_SIZE when > SEV is active? struct pvclock_vsyscall_time_info is 32 bytes so we > could handle the max of 8192 CPUs with 256kb of data (252kb if you > subtract the pre-existing 4k page), i.e. the SEV case wouldn't need > additional memory beyond the 2mb page that's reserved for __decrypted. > The non-SEV case could do free_kernel_image_pages() on the unused > array (which would need to be page sized) so it wouldn't waste memory. Sure, we could use unused memory range from .data..decrypted section for cpu > HVC_BOOT_ARRAY_SIZE when SEV is active. I will rework the patch. -Brijesh
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index 1e67646..08f5f8a 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -28,6 +28,7 @@ #include <linux/sched/clock.h> #include <linux/mm.h> #include <linux/slab.h> +#include <linux/set_memory.h> #include <asm/hypervisor.h> #include <asm/mem_encrypt.h> @@ -61,8 +62,8 @@ early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall); (PAGE_SIZE / sizeof(struct pvclock_vsyscall_time_info)) static struct pvclock_vsyscall_time_info - hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __aligned(PAGE_SIZE); -static struct pvclock_wall_clock wall_clock; + hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __decrypted __aligned(PAGE_SIZE); +static struct pvclock_wall_clock wall_clock __decrypted; static DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu); static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void) @@ -267,10 +268,29 @@ static int kvmclock_setup_percpu(unsigned int cpu) return 0; /* Use the static page for the first CPUs, allocate otherwise */ - if (cpu < HVC_BOOT_ARRAY_SIZE) + if (cpu < HVC_BOOT_ARRAY_SIZE) { p = &hv_clock_boot[cpu]; - else - p = kzalloc(sizeof(*p), GFP_KERNEL); + } else { + int rc; + unsigned int sz = sizeof(*p); + + if (sev_active()) + sz = PAGE_ALIGN(sz); + + p = kzalloc(sz, GFP_KERNEL); + + /* + * The physical address of per-cpu variable will be shared with + * the hypervisor. Let's clear the C-bit before we assign the + * memory to per_cpu variable. + */ + if (p && sev_active()) { + rc = set_memory_decrypted((unsigned long)p, sz >> PAGE_SHIFT); + if (rc) + return rc; + memset(p, 0, sz); + } + } per_cpu(hv_clock_per_cpu, cpu) = p; return p ? 0 : -ENOMEM;