From bd22f5cfcfe8f68bf43b72daf4530cd7eedc9b7a Mon Sep 17 00:00:00 2001 From: Andre Przywara Date: Thu, 31 Mar 2011 16:58:49 +0200 Subject: [PATCH] KVM: move and fix substitue search for missing CPUID entries If KVM cannot find an exact match for a requested CPUID leaf, the code will try to find the closest match instead of simply confessing it's failure. The implementation was meant to satisfy the CPUID specification, but did not properly check for extended and standard leaves and also didn't account for the index subleaf. Beside that this rule only applies to CPUID intercepts, which is not the only user of the kvm_find_cpuid_entry() function. So fix this algorithm and call it from kvm_emulate_cpuid(). This fixes a crash of newer Linux kernels as KVM guests on AMD Bulldozer CPUs, where bogus values were returned in response to a CPUID intercept. Signed-off-by: Andre Przywara Signed-off-by: Avi Kivity --- arch/x86/kvm/x86.c | 31 +++++++++++++++++++++++++------ 1 file changed, 25 insertions(+), 6 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 4a1ba05f7af..934b4c6b0bf 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4958,12 +4958,6 @@ struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu, best = e; break; } - /* - * Both basic or both extended? - */ - if (((e->function ^ function) & 0x80000000) == 0) - if (!best || e->function > best->function) - best = e; } return best; } @@ -4983,6 +4977,27 @@ not_found: return 36; } +/* + * If no match is found, check whether we exceed the vCPU's limit + * and return the content of the highest valid _standard_ leaf instead. + * This is to satisfy the CPUID specification. + */ +static struct kvm_cpuid_entry2* check_cpuid_limit(struct kvm_vcpu *vcpu, + u32 function, u32 index) +{ + struct kvm_cpuid_entry2 *maxlevel; + + maxlevel = kvm_find_cpuid_entry(vcpu, function & 0x80000000, 0); + if (!maxlevel || maxlevel->eax >= function) + return NULL; + if (function & 0x80000000) { + maxlevel = kvm_find_cpuid_entry(vcpu, 0, 0); + if (!maxlevel) + return NULL; + } + return kvm_find_cpuid_entry(vcpu, maxlevel->eax, index); +} + void kvm_emulate_cpuid(struct kvm_vcpu *vcpu) { u32 function, index; @@ -4995,6 +5010,10 @@ void kvm_emulate_cpuid(struct kvm_vcpu *vcpu) kvm_register_write(vcpu, VCPU_REGS_RCX, 0); kvm_register_write(vcpu, VCPU_REGS_RDX, 0); best = kvm_find_cpuid_entry(vcpu, function, index); + + if (!best) + best = check_cpuid_limit(vcpu, function, index); + if (best) { kvm_register_write(vcpu, VCPU_REGS_RAX, best->eax); kvm_register_write(vcpu, VCPU_REGS_RBX, best->ebx); -- 2.46.0