mirrors/linux
2
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-05-10 15:13:44 -04:00
Code Issues Packages Projects Releases Wiki Activity

KVM: x86: Explicitly do runtime CPUID updates "after" initial setup

Browse Source 
Explicitly perform runtime CPUID adjustments as part of the "after set
CPUID" flow to guard against bugs where KVM consumes stale vCPU/CPUID
state during kvm_update_cpuid_runtime().  E.g. see commit 4736d85f0d
("KVM: x86: Use actual kvm_cpuid.base for clearing KVM_FEATURE_PV_UNHALT").

Whacking each mole individually is not sustainable or robust, e.g. while
the aforemention commit fixed KVM's PV features, the same issue lurks for
Xen and Hyper-V features, Xen and Hyper-V simply don't have any runtime
features (though spoiler alert, neither should KVM).

Updating runtime features in the "full" path will also simplify adding a
snapshot of the guest's capabilities, i.e. of caching the intersection of
guest CPUID and kvm_cpu_caps (modulo a few edge cases).

Link: https://lore.kernel.org/r/20241128013424.4096668-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2024-11-27 17:33:31 -08:00
parent 85e5ba83c0
commit ec3d4440b2
1 changed files with 16 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

18
arch/x86/kvm/cpuid.c
View File

@@ -178,6 +178,9 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
return fpu_enable_guest_xfd_features(&vcpu->arch.guest_fpu, xfeatures);
}
static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *entries,
int nent);
/* Check whether the supplied CPUID data is equal to what is already set for the vCPU. */
static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
int nent)
@@ -185,6 +188,17 @@ static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2
struct kvm_cpuid_entry2 *orig;
int i;
/*
* Apply runtime CPUID updates to the incoming CPUID entries to avoid
* false positives due mismatches on KVM-owned feature flags. Note,
* runtime CPUID updates may consume other CPUID-driven vCPU state,
* e.g. KVM or Xen CPUID bases. Updating runtime state before full
* CPUID processing is functionally correct only because any change in
* CPUID is disallowed, i.e. using stale data is ok because the below
* checks will reject the change.
*/
__kvm_update_cpuid_runtime(vcpu, e2, nent);
if (nent != vcpu->arch.cpuid_nent)
return -EINVAL;
@@ -369,6 +383,8 @@ void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
bitmap_zero(vcpu->arch.governed_features.enabled,
KVM_MAX_NR_GOVERNED_FEATURES);
kvm_update_cpuid_runtime(vcpu);
/*
* If TDP is enabled, let the guest use GBPAGES if they're supported in
* hardware. The hardware page walker doesn't let KVM disable GBPAGES,
@@ -450,8 +466,6 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
{
int r;
__kvm_update_cpuid_runtime(vcpu, e2, nent);
/*
* KVM does not correctly handle changing guest CPUID after KVM_RUN, as
* MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't