Re: [PATCH 2/5] KVM: arm64: Avoid mapping size adjustment on permission fault
From: Alexandru Elisei <hidden>
Date: 2021-07-23 15:54:39
Also in:
kvm, kvmarm, linux-mm
Hi Marc, On 7/17/21 10:55 AM, Marc Zyngier wrote:
quoted hunk ↗ jump to hunk
Since we only support PMD-sized mappings for THP, getting a permission fault on a level that results in a mapping being larger than PAGE_SIZE is a sure indication that we have already upgraded our mapping to a PMD. In this case, there is no need to try and parse userspace page tables, as the fault information already tells us everything. Signed-off-by: Marc Zyngier <maz@kernel.org> --- arch/arm64/kvm/mmu.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index db6314b93e99..c036a480ca27 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c@@ -1088,9 +1088,14 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, * If we are not forced to use page mapping, check if we are * backed by a THP and thus use block mapping if possible. */ - if (vma_pagesize == PAGE_SIZE && !(force_pte || device)) - vma_pagesize = transparent_hugepage_adjust(kvm, memslot, hva, - &pfn, &fault_ipa); + if (vma_pagesize == PAGE_SIZE && !force_pte) {
Looks like now it's possible to call transparent_hugepage_adjust() for devices (if
fault_status != FSC_PERM). Commit 2aa53d68cee6 ("KVM: arm64: Try stage2 block
mapping for host device MMIO") makes a good case for the !device check. Was the
check removed unintentionally?
+ if (fault_status == FSC_PERM && fault_granule > PAGE_SIZE) + vma_pagesize = fault_granule; + else + vma_pagesize = transparent_hugepage_adjust(kvm, memslot, + hva, &pfn, + &fault_ipa); + }
This change makes sense to me - we can only get stage 2 permission faults on a leaf entry since stage 2 tables don't have the APTable/XNTable/PXNTable bits. The biggest block mapping size that we support at stage 2 is PMD size (from transparent_hugepage_adjust()), therefore if fault_granule is larger than PAGE_SIZE, then it must be PMD_SIZE. Thanks, Alex
if (fault_status != FSC_PERM && !device && kvm_has_mte(kvm)) {
/* Check the VMM hasn't introduced a new VM_SHARED VMA */_______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel