From: Sean Christopherson <sean.j.christopherson@intel.com>
To: "Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
James Harvey <jamespharvey20@gmail.com>,
Alex Willamson <alex.williamson@redhat.com>
Subject: [PATCH 02/11] KVM: x86/mmu: Treat invalid shadow pages as obsolete
Date: Thu, 12 Sep 2019 19:46:03 -0700 [thread overview]
Message-ID: <20190913024612.28392-3-sean.j.christopherson@intel.com> (raw)
In-Reply-To: <20190913024612.28392-1-sean.j.christopherson@intel.com>
Treat invalid shadow pages as obsolete to fix a bug where an obsolete
and invalid page with a non-zero root count could become non-obsolete
due to mmu_valid_gen wrapping. The bug is largely theoretical with the
current code base, as an unsigned long will effectively never wrap on
64-bit KVM, and userspace would have to deliberately stall a vCPU in
order to keep an obsolete invalid page on the active list while
simultaneously modifying memslots billions of times to trigger a wrap.
The obvious alternative is to use a 64-bit value for mmu_valid_gen,
but it's actually desirable to go in the opposite direction, i.e. using
a smaller 8-bit value to reduce KVM's memory footprint by 8 bytes per
shadow page, and relying on proper treatment of invalid pages instead of
preventing the generation from wrapping.
Note, "Fixes" points at a commit that was at one point reverted, but has
since been restored.
Fixes: 5304b8d37c2a5 ("KVM: MMU: fast invalidate all pages")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/mmu.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 5ac5e3f50f92..373e6f052f9f 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2252,7 +2252,7 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
#define for_each_valid_sp(_kvm, _sp, _gfn) \
hlist_for_each_entry(_sp, \
&(_kvm)->arch.mmu_page_hash[kvm_page_table_hashfn(_gfn)], hash_link) \
- if (is_obsolete_sp((_kvm), (_sp)) || (_sp)->role.invalid) { \
+ if (is_obsolete_sp((_kvm), (_sp))) { \
} else
#define for_each_gfn_indirect_valid_sp(_kvm, _sp, _gfn) \
@@ -2311,7 +2311,8 @@ static void mmu_audit_disable(void) { }
static bool is_obsolete_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
{
- return unlikely(sp->mmu_valid_gen != kvm->arch.mmu_valid_gen);
+ return sp->role.invalid ||
+ unlikely(sp->mmu_valid_gen != kvm->arch.mmu_valid_gen);
}
static bool kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
--
2.22.0
next prev parent reply other threads:[~2019-09-13 2:46 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-13 2:46 [PATCH 00/11] KVM: x86/mmu: Restore fast invalidate/zap flow Sean Christopherson
2019-09-13 2:46 ` [PATCH 01/11] KVM: x86/mmu: Reintroduce fast invalidate/zap for flushing memslot Sean Christopherson
2019-09-13 2:46 ` Sean Christopherson [this message]
2019-09-13 2:46 ` [PATCH 03/11] KVM: x86/mmu: Use fast invalidate mechanism to zap MMIO sptes Sean Christopherson
2019-09-13 2:46 ` [PATCH 04/11] KVM: x86/mmu: Revert "Revert "KVM: MMU: show mmu_valid_gen in shadow page related tracepoints"" Sean Christopherson
2019-09-13 2:46 ` [PATCH 05/11] KVM: x86/mmu: Revert "Revert "KVM: MMU: add tracepoint for kvm_mmu_invalidate_all_pages"" Sean Christopherson
2019-09-13 2:46 ` [PATCH 06/11] KVM: x86/mmu: Revert "Revert "KVM: MMU: zap pages in batch"" Sean Christopherson
2019-09-13 2:46 ` [PATCH 07/11] KVM: x86/mmu: Revert "Revert "KVM: MMU: collapse TLB flushes when zap all pages"" Sean Christopherson
2019-09-13 2:46 ` [PATCH 08/11] KVM: x86/mmu: Revert "Revert "KVM: MMU: reclaim the zapped-obsolete page first"" Sean Christopherson
2019-09-13 2:46 ` [PATCH 09/11] KVM: x86/mmu: Revert "KVM: x86/mmu: Remove is_obsolete() call" Sean Christopherson
2019-09-13 2:46 ` [PATCH 10/11] KVM: x86/mmu: Explicitly track only a single invalid mmu generation Sean Christopherson
2019-09-13 2:46 ` [PATCH 11/11] KVM: x86/mmu: Skip invalid pages during zapping iff root_count is zero Sean Christopherson
2019-09-13 22:11 ` [PATCH 00/11] KVM: x86/mmu: Restore fast invalidate/zap flow Paolo Bonzini
2019-09-16 17:07 ` Alex Williamson
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