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X-Received-From: 2607:f8b0:400e:c00::241 Subject: [Qemu-devel] [PATCH 6/7] KVM: MMU: clarify fast_pf_fix_direct_spte X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Xiao Guangrong , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: Xiao Guangrong The writable spte can not be locklessly fixed and add a WARN_ON() to trigger the warning if something out of our mind happens, that is good for us to track if the log for writable spte is missed on the fast path Signed-off-by: Xiao Guangrong --- arch/x86/kvm/mmu.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index ad6ee46..f6a74e7 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -3225,6 +3225,15 @@ fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, WARN_ON(!sp->role.direct); /* + * the original spte can not be writable as only the spte which + * fulfills is_access_track_spte() or + * spte_can_locklessly_be_made_writable() can be locklessly fixed, + * for the former, the W bit is always cleared, for the latter, + * there is nothing to do if it is already writable. + */ + WARN_ON(is_writable_pte(old_spte)); + + /* * Theoretically we could also set dirty bit (and flush TLB) here in * order to eliminate unnecessary PML logging. See comments in * set_spte. But fast_page_fault is very unlikely to happen with PML @@ -3239,7 +3248,7 @@ fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, if (cmpxchg64(sptep, old_spte, new_spte) != old_spte) return false; - if (is_writable_pte(new_spte) && !is_writable_pte(old_spte)) { + if (is_writable_pte(new_spte)) { /* * The gfn of direct spte is stable since it is * calculated by sp->gfn.