linux-kernel - [PATCH V2] kvm x86/mmu: use KVM_REQ_MMU

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Message-Id: <20200902135421.31158-1-jiangshanlai@gmail.com>
Date:   Wed,  2 Sep 2020 21:54:21 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        kvm@...r.kernel.org
Subject: [PATCH V2] kvm x86/mmu: use KVM_REQ_MMU_SYNC to sync when needed

From: Lai Jiangshan <laijs@...ux.alibaba.com>

When kvm_mmu_get_page() gets a page with unsynced children, the spt
pagetable is unsynchronized with the guest pagetable. But the
guest might not issue a "flush" operation on it when the pagetable
entry is changed from zero or other cases. The hypervisor has the 
responsibility to synchronize the pagetables.

The linux kernel behaves as above for many years, But
8c8560b83390("KVM: x86/mmu: Use KVM_REQ_TLB_FLUSH_CURRENT for MMU specific flushes)
inadvertently included a line of code to change it without giving any
reason in the changelog. It is clear that the commit's intention was to
change KVM_REQ_TLB_FLUSH -> KVM_REQ_TLB_FLUSH_CURRENT, so we don't
unneedlesly flush other contexts but one of the hunks changed
nearby KVM_REQ_MMU_SYNC instead.

The this patch changes it back.

Link: https://lore.kernel.org/lkml/20200320212833.3507-26-sean.j.christopherson@intel.com/
Cc: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
Changed from v1:
	update patch description

 arch/x86/kvm/mmu/mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4e03841f053d..9a93de921f2b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2468,7 +2468,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 		}

 		if (sp->unsync_children)
-			kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
+			kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);

 		__clear_sp_write_flooding_count(sp);

-- 
2.19.1.6.gb485710b