linux-kernel - [PATCH 1/7] KVM: x86: Use guest MAXPHYADDR from CPUID.0x8000

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Date:   Wed, 23 Jun 2021 16:05:46 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Peter Gonda <pgonda@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH 1/7] 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@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.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 b4da665bb892..4b2f8c6b41e8 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);
-- 
2.32.0.288.g62a8d224e6-goog