linux-kernel - [PATCH 2/2] KVM: X86: Fix loss of CR3_PCID

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Message-Id: <1526181854-3631-1-git-send-email-wanpengli@tencent.com>
Date:   Sat, 12 May 2018 20:24:14 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Junaid Shahid <junaids@...gle.com>
Subject: [PATCH 2/2] KVM: X86: Fix loss of CR3_PCID_INVD bit when guest writes CR3

From: Wanpeng Li <wanpengli@...cent.com>

SDM volume 3, section 4.10.4:

* MOV to CR3. The behavior of the instruction depends on the value of CR4.PCIDE:
— If CR4.PCIDE = 1 and bit 63 of the instruction’s source operand is 1, the 
  instruction is not required to invalidate any TLB entries or entries in 
  paging-structure caches.

The CR3_PCID_INVD bit should not be removed if CR4.PCIDE = 1 when guest writes 
CR3, this patch fixes it.

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Junaid Shahid <junaids@...gle.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kvm/x86.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9a90668..438f140 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -849,11 +849,13 @@ EXPORT_SYMBOL_GPL(kvm_set_cr4);
 
 int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 {
+	unsigned long cr3_check = cr3;
+
 #ifdef CONFIG_X86_64
 	bool pcid_enabled = kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE);
 
 	if (pcid_enabled)
-		cr3 &= ~CR3_PCID_INVD;
+		cr3_check &= ~CR3_PCID_INVD;
 #endif
 
 	if (cr3 == kvm_read_cr3(vcpu) && !pdptrs_changed(vcpu)) {
@@ -863,7 +865,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 	}
 
 	if (is_long_mode(vcpu) &&
-	    (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 63)))
+	    (cr3_check & rsvd_bits(cpuid_maxphyaddr(vcpu), 63)))
 		return 1;
 	else if (is_pae(vcpu) && is_paging(vcpu) &&
 		   !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))
-- 
2.7.4