Re: [PATCH v12 54/84] KVM: arm64: Mark "struct page" pfns accessed/dirty before dropping mmu_lock
From: Oliver Upton <hidden>
Date: 2024-08-05 23:26:06
Also in:
kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-mips, linux-riscv, lkml, loongarch
[+cc Fuad]
Fuad, you mentioned in commit 9c30fc615daa ("KVM: arm64: Move setting
the page as dirty out of the critical section") that restructuring
around the MMU lock was helpful for reuse (presumably for pKVM), but I
lack the context there.
On Fri, Jul 26, 2024 at 04:52:03PM -0700, Sean Christopherson wrote:Mark pages/folios accessed+dirty prior to dropping mmu_lock, as marking a page/folio dirty after it has been written back can make some filesystems unhappy (backing KVM guests will such filesystem files is uncommon, and
typo: s/will/with/
quoted hunk ↗ jump to hunk
the race is minuscule, hence the lack of complaints). See the link below for details. This will also allow converting arm64 to kvm_release_faultin_page(), which requires that mmu_lock be held (for the aforementioned reason). Link: https://lore.kernel.org/all/cover.1683044162.git.lstoakes@gmail.com (local) Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/arm64/kvm/mmu.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 22ee37360c4e..ce13c3d884d5 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c@@ -1685,15 +1685,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, } out_unlock: + if (writable && !ret) + kvm_set_pfn_dirty(pfn);
I'm guessing you meant kvm_release_pfn_dirty() here, because this leaks a reference.
+ else
+ kvm_release_pfn_clean(pfn);
+
read_unlock(&kvm->mmu_lock);
/* Mark the page dirty only if the fault is handled successfully */
- if (writable && !ret) {
- kvm_set_pfn_dirty(pfn);
+ if (writable && !ret)
mark_page_dirty_in_slot(kvm, memslot, gfn);
- }
- kvm_release_pfn_clean(pfn);
return ret != -EAGAIN ? ret : 0;
}
--
2.46.0.rc1.232.g9752f9e123-goog-- Thanks, Oliver