Re: [PATCH v4 4/4] KVM: mmu: remove over-aggressive warnings
From: Sean Christopherson <seanjc@google.com>
Date: 2021-10-13 00:02:56
Also in:
kvm, kvmarm, lkml
On Wed, Sep 29, 2021, David Stevens wrote:
quoted hunk ↗ jump to hunk
From: David Stevens <redacted> Remove two warnings that require ref counts for pages to be non-zero, as mapped pfns from follow_pfn may not have an initialized ref count. Signed-off-by: David Stevens <redacted> --- arch/x86/kvm/mmu/mmu.c | 7 ------- virt/kvm/kvm_main.c | 2 +- 2 files changed, 1 insertion(+), 8 deletions(-)diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 5a1adcc9cfbc..3b469df63bcf 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c@@ -617,13 +617,6 @@ static int mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep) pfn = spte_to_pfn(old_spte); - /* - * KVM does not hold the refcount of the page used by - * kvm mmu, before reclaiming the page, we should - * unmap it from mmu first. - */ - WARN_ON(!kvm_is_reserved_pfn(pfn) && !page_count(pfn_to_page(pfn)));
Have you actually observed false positives with this WARN? I would expect anything without a struct page to get filtered out by !kvm_is_reserved_pfn(pfn). If you have observed false positives, I would strongly prefer we find a way to keep the page_count() sanity check, it has proven very helpful in the past in finding/debugging bugs during MMU development.
- if (is_accessed_spte(old_spte)) kvm_set_pfn_accessed(pfn);
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