linux-kernel - [PATCH v2 1/2] KVM: x86: Introduce cr3_lm_rsvd_bits in kvm_vcpu

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Message-ID: <160521947657.32054.3264016688005356563.stgit@bmoger-ubuntu>
Date:   Thu, 12 Nov 2020 16:17:56 -0600
From:   Babu Moger <babu.moger@....com>
To:     pbonzini@...hat.com
Cc:     junaids@...gle.com, wanpengli@...cent.com, kvm@...r.kernel.org,
        joro@...tes.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        sean.j.christopherson@...el.com, mingo@...hat.com, bp@...en8.de,
        hpa@...or.com, tglx@...utronix.de, vkuznets@...hat.com,
        jmattson@...gle.com
Subject: [PATCH v2 1/2] KVM: x86: Introduce cr3_lm_rsvd_bits in kvm_vcpu_arch

SEV guests fail to boot on a system that supports the PCID feature.

While emulating the RSM instruction, KVM reads the guest CR3
and calls kvm_set_cr3(). If the vCPU is in the long mode,
kvm_set_cr3() does a sanity check for the CR3 value. In this case,
it validates whether the value has any reserved bits set. The
reserved bit range is 63:cpuid_maxphysaddr(). When AMD memory
encryption is enabled, the memory encryption bit is set in the CR3
value. The memory encryption bit may fall within the KVM reserved
bit range, causing the KVM emulation failure.

Introduce a new field cr3_lm_rsvd_bits in kvm_vcpu_arch which will
cache the reserved bits in the CR3 value. This will be initialized
to rsvd_bits(cpuid_maxphyaddr(vcpu), 63).

If the architecture has any special bits(like AMD SEV encryption bit)
that needs to be masked from the reserved bits, should be cleared
in vendor specific kvm_x86_ops.vcpu_after_set_cpuid handler.

Fixes: a780a3ea628268b2 ("KVM: X86: Fix reserved bits check for MOV to CR3")
Signed-off-by: Babu Moger <babu.moger@....com>
---
 arch/x86/include/asm/kvm_host.h |    1 +
 arch/x86/kvm/cpuid.c            |    2 ++
 arch/x86/kvm/x86.c              |    2 +-
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d44858b69353..324ddd7fd0aa 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -639,6 +639,7 @@ struct kvm_vcpu_arch {
 	int cpuid_nent;
 	struct kvm_cpuid_entry2 *cpuid_entries;
 
+	unsigned long cr3_lm_rsvd_bits;
 	int maxphyaddr;
 	int max_tdp_level;
 
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 06a278b3701d..cb52485cc507 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -169,6 +169,8 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	vcpu->arch.cr4_guest_rsvd_bits =
 	    __cr4_reserved_bits(guest_cpuid_has, vcpu);
 
+	vcpu->arch.cr3_lm_rsvd_bits = rsvd_bits(cpuid_maxphyaddr(vcpu), 63);
+
 	/* Invoke the vendor callback only after the above state is updated. */
 	kvm_x86_ops.vcpu_after_set_cpuid(vcpu);
 }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f5ede41bf9e6..ff55e33b268b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1042,7 +1042,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 	}
 
 	if (is_long_mode(vcpu) &&
-	    (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 63)))
+	    (cr3 & vcpu->arch.cr3_lm_rsvd_bits))
 		return 1;
 	else if (is_pae_paging(vcpu) &&
 		 !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))