Hi Steven, On Fri, Mar 12, 2021 at 03:18:57PM +0000, Steven Price wrote: > A KVM guest could store tags in a page even if the VMM hasn't mapped > the page with PROT_MTE. So when restoring pages from swap we will > need to check to see if there are any saved tags even if !pte_tagged(). > > However don't check pages which are !pte_valid_user() as these will > not have been swapped out. > > Signed-off-by: Steven Price <steven.price@xxxxxxx> > --- > arch/arm64/include/asm/pgtable.h | 2 +- > arch/arm64/kernel/mte.c | 16 ++++++++++++---- > 2 files changed, 13 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index e17b96d0e4b5..84166625c989 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -312,7 +312,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, > __sync_icache_dcache(pte); > > if (system_supports_mte() && > - pte_present(pte) && pte_tagged(pte) && !pte_special(pte)) > + pte_present(pte) && pte_valid_user(pte) && !pte_special(pte)) > mte_sync_tags(ptep, pte); With the EPAN patches queued in for-next/epan, pte_valid_user() disappeared as its semantics weren't very clear. So this relies on the set_pte_at() being done on the VMM address space. I wonder, if the VMM did an mprotect(PROT_NONE), can the VM still access it via stage 2? If yes, the pte_valid_user() test wouldn't work. We need something like pte_present() && addr <= user_addr_max(). BTW, ignoring virtualisation, can we ever bring a page in from swap on a PROT_NONE mapping (say fault-around)? It's not too bad if we keep the metadata around for when the pte becomes accessible but I suspect we remove it if the page is removed from swap. -- Catalin _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
