From 4bf48e3c0aafd32b960d341c4925b48f416f14a5 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Wed, 23 Jun 2021 16:05:46 -0700
Subject: [PATCH] KVM: x86: Use guest MAXPHYADDR from CPUID.0x8000_0008 iff TDP
is enabled
Ignore the guest MAXPHYADDR reported by CPUID.0x8000_0008 if TDP, i.e.
NPT, is disabled, and instead use the host's MAXPHYADDR. Per AMD'S APM:
Maximum guest physical address size in bits. This number applies only
to guests using nested paging. When this field is zero, refer to the
PhysAddrSize field for the maximum guest physical address size.
Fixes: 24c82e576b78 ("KVM: Sanitize cpuid")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210623230552.4027702-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/cpuid.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index c42613cfb5ba6..1a4217b3e1855 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -940,8 +940,14 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
unsigned virt_as = max((entry->eax >> 8) & 0xff, 48U);
unsigned phys_as = entry->eax & 0xff;
- if (!g_phys_as)
+ /*
+ * Use bare metal's MAXPHADDR if the CPU doesn't report guest
+ * MAXPHYADDR separately, or if TDP (NPT) is disabled, as the
+ * guest version "applies only to guests using nested paging".
+ */
+ if (!g_phys_as || !tdp_enabled)
g_phys_as = phys_as;
+
entry->eax = g_phys_as | (virt_as << 8);
entry->edx = 0;
cpuid_entry_override(entry, CPUID_8000_0008_EBX);
--
GitLab