| Message ID | 20230809164633.1556126-1-alexghiti@rivosinc.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [-fixes] mm: Add a call to flush_cache_vmap() in vmap_pfn() | expand |
On Wed, 9 Aug 2023 18:46:33 +0200 Alexandre Ghiti <alexghiti@rivosinc.com> wrote: > flush_cache_vmap() must be called after new vmalloc mappings are > installed in the page table in order to allow architectures to make sure > the new mapping is visible. Thanks. What are the user-visible effects of this bug?
On Wed, Aug 09, 2023 at 06:46:33PM +0200, Alexandre Ghiti wrote: > flush_cache_vmap() must be called after new vmalloc mappings are > installed in the page table in order to allow architectures to make sure > the new mapping is visible. Looks good. I somehow vaguely remember seing a patch like this floating around before as part of a series, but if that didn't make it it certainly should now. Reviewed-by: Christoph Hellwig <hch@lst.de>
Hi Andrew, On Wed, Aug 9, 2023 at 8:46 PM Andrew Morton <akpm@linux-foundation.org> wrote: > > On Wed, 9 Aug 2023 18:46:33 +0200 Alexandre Ghiti <alexghiti@rivosinc.com> wrote: > > > flush_cache_vmap() must be called after new vmalloc mappings are > > installed in the page table in order to allow architectures to make sure > > the new mapping is visible. > > Thanks. What are the user-visible effects of this bug? It could lead to a panic since on some architectures (like powerpc), the page table walker could see the wrong pte value and trigger a spurious page fault that can not be resolved (see commit f1cb8f9beba8 ("powerpc/64s/radix: avoid ptesync after set_pte and ptep_set_access_flags")). But actually the patch is aiming at riscv: the riscv specification allows the caching of invalid entries in the TLB, and since we recently removed the vmalloc page fault handling, we now need to emit a tlb shootdown whenever a new vmalloc mapping is emitted (https://lore.kernel.org/linux-riscv/20230725132246.817726-1-alexghiti@rivosinc.com/). That's a temporary solution, there are ways to avoid that :) Thanks, Alex
On Wed, 09 Aug 2023 15:25:19 PDT (-0700), Christoph Hellwig wrote: > On Wed, Aug 09, 2023 at 06:46:33PM +0200, Alexandre Ghiti wrote: >> flush_cache_vmap() must be called after new vmalloc mappings are >> installed in the page table in order to allow architectures to make sure >> the new mapping is visible. > > Looks good. I somehow vaguely remember seing a patch like this floating > around before as part of a series, but if that didn't make it it > certainly should now. > > Reviewed-by: Christoph Hellwig <hch@lst.de> I think we're likely to end up with performance problems around here, but at least it's correct. If someone has performance Dylan: this fixes your breakage as well, right? I've queued it up for testing, but I doubt QEMU would find any issues here. My build box has been slow lately, but it should end up in fixes later today.
On Thu, 10 Aug 2023 08:13:56 PDT (-0700), Palmer Dabbelt wrote: > On Wed, 09 Aug 2023 15:25:19 PDT (-0700), Christoph Hellwig wrote: >> On Wed, Aug 09, 2023 at 06:46:33PM +0200, Alexandre Ghiti wrote: >>> flush_cache_vmap() must be called after new vmalloc mappings are >>> installed in the page table in order to allow architectures to make sure >>> the new mapping is visible. >> >> Looks good. I somehow vaguely remember seing a patch like this floating >> around before as part of a series, but if that didn't make it it >> certainly should now. >> >> Reviewed-by: Christoph Hellwig <hch@lst.de> > > I think we're likely to end up with performance problems around here, > but at least it's correct. If someone has performance > > Dylan: this fixes your breakage as well, right? > > I've queued it up for testing, but I doubt QEMU would find any issues > here. My build box has been slow lately, but it should end up in fixes > later today. Sorry about that, I'm in the wrong thread -- I meant to be over here <https://lore.kernel.org/all/20230725132246.817726-1-alexghiti@rivosinc.com/>. Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com> Acked-by: Palmer Dabbelt <palmer@rivosinc.com> but I'm not taking this via the RISC-V tree unless someone asks.
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 93cf99aba335..228a4a5312f2 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2979,6 +2979,10 @@ void *vmap_pfn(unsigned long *pfns, unsigned int count, pgprot_t prot) free_vm_area(area); return NULL; } + + flush_cache_vmap((unsigned long)area->addr, + (unsigned long)area->addr + count * PAGE_SIZE); + return area->addr; } EXPORT_SYMBOL_GPL(vmap_pfn);
flush_cache_vmap() must be called after new vmalloc mappings are installed in the page table in order to allow architectures to make sure the new mapping is visible. Fixes: 3e9a9e256b1e ("mm: add a vmap_pfn function") Reported-by: Dylan Jhong <dylan@andestech.com> Closes: https://lore.kernel.org/linux-riscv/ZMytNY2J8iyjbPPy@atctrx.andestech.com/ Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> --- mm/vmalloc.c | 4 ++++ 1 file changed, 4 insertions(+)