| Message ID | 20250110110023.2963795-3-aneesh.kumar@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Add support for NoTagAccess memory attribute | expand |
On Fri, Jan 10, 2025 at 04:30:18PM +0530, Aneesh Kumar K.V (Arm) wrote: > commit d77e59a8fccd ("arm64: mte: Lock a page for MTE tag > initialisation") updated the locking such the kernel now allows > VM_SHARED mapping with MTE. Update the code comment to reflect this. > > Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org> > --- > arch/arm64/kvm/mmu.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index c9d46ad57e52..eb8220a409e1 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1391,11 +1391,11 @@ static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva) > * able to see the page's tags and therefore they must be initialised first. If > * PG_mte_tagged is set, tags have already been initialised. > * > - * The race in the test/set of the PG_mte_tagged flag is handled by: > - * - preventing VM_SHARED mappings in a memslot with MTE preventing two VMs > - * racing to santise the same page > - * - mmap_lock protects between a VM faulting a page in and the VMM performing > - * an mprotect() to add VM_MTE > + * The race in the test/set of the PG_mte_tagged flag is handled by using > + * PG_mte_lock and PG_mte_tagged together. if PG_mte_lock is found unset, we can > + * go ahead and clear the page tags. if PG_mte_lock is found set, then the page > + * tags are already cleared or there is a parallel tag clearing is going on. We ^^^^^^^^ remove this (or the other 'is') > + * wait for the parallel tag clear to finish by waiting on PG_mte_tagged bit. > */ I don't think we need to describe the behaviour of set_page_mte_tagged() and try_page_mte_tagging() in here. How the locking works for tagged pages was hidden in those functions with their own documentation. I would just remove this whole paragraph here, just leave the first one stating that the tags must be initialised if not already done so.
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index c9d46ad57e52..eb8220a409e1 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1391,11 +1391,11 @@ static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva) * able to see the page's tags and therefore they must be initialised first. If * PG_mte_tagged is set, tags have already been initialised. * - * The race in the test/set of the PG_mte_tagged flag is handled by: - * - preventing VM_SHARED mappings in a memslot with MTE preventing two VMs - * racing to santise the same page - * - mmap_lock protects between a VM faulting a page in and the VMM performing - * an mprotect() to add VM_MTE + * The race in the test/set of the PG_mte_tagged flag is handled by using + * PG_mte_lock and PG_mte_tagged together. if PG_mte_lock is found unset, we can + * go ahead and clear the page tags. if PG_mte_lock is found set, then the page + * tags are already cleared or there is a parallel tag clearing is going on. We + * wait for the parallel tag clear to finish by waiting on PG_mte_tagged bit. */ static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn, unsigned long size)
commit d77e59a8fccd ("arm64: mte: Lock a page for MTE tag initialisation") updated the locking such the kernel now allows VM_SHARED mapping with MTE. Update the code comment to reflect this. Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org> --- arch/arm64/kvm/mmu.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)