KVM: x86: use CPUID to locate host page table reserved bits

The comment in kvm_get_shadow_phys_bits refers to MKTME, but the same is actually
true of SME and SEV.  Just use CPUID[0x8000_0008].EAX[7:0] unconditionally if
available, it is simplest and works even if memory is not encrypted.

Cc: stable@vger.kernel.org
Reported-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6f92b40d798cab7d4b9f4a451621319e687e29df..1e4ee4f8de5f0dfcac982f575095675d8678631b 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -538,16 +538,20 @@ EXPORT_SYMBOL_GPL(kvm_mmu_set_mask_ptes);
 static u8 kvm_get_shadow_phys_bits(void)
 {
        /*
-        * boot_cpu_data.x86_phys_bits is reduced when MKTME is detected
-        * in CPU detection code, but MKTME treats those reduced bits as
-        * 'keyID' thus they are not reserved bits. Therefore for MKTME
-        * we should still return physical address bits reported by CPUID.
+        * boot_cpu_data.x86_phys_bits is reduced when MKTME or SME are detected
+        * in CPU detection code, but the processor treats those reduced bits as
+        * 'keyID' thus they are not reserved bits. Therefore KVM needs to look at
+        * the physical address bits reported by CPUID.
         */
-       if (!boot_cpu_has(X86_FEATURE_TME) ||
-           WARN_ON_ONCE(boot_cpu_data.extended_cpuid_level < 0x80000008))
-               return boot_cpu_data.x86_phys_bits;
+       if (likely(boot_cpu_data.extended_cpuid_level >= 0x80000008))
+               return cpuid_eax(0x80000008) & 0xff;
 
-       return cpuid_eax(0x80000008) & 0xff;
+       /*
+        * Quite weird to have VMX or SVM but not MAXPHYADDR; probably a VM with
+        * custom CPUID.  Proceed with whatever the kernel found since these features
+        * aren't virtualizable (SME/SEV also require CPUIDs higher than 0x80000008).
+        */
+       return boot_cpu_data.x86_phys_bits;
 }
 
 static void kvm_mmu_reset_all_pte_masks(void)