The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
Possible dependencies:
45e966fcca03 ("KVM: x86: Do not return host topology information from KVM_GET_SUPPORTED_CPUID")
cde363ab7ca7 ("Documentation: KVM: add API issues section")
ba7bb663f554 ("KVM: x86: Provide per VM capability for disabling PMU virtualization")
4dfc4ec2b7f5 ("Merge branch 'kvm-ppc-cap-210' into kvm-next-5.18")
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 45e966fcca03ecdcccac7cb236e16eea38cc18af Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Sat, 22 Oct 2022 04:17:53 -0400
Subject: [PATCH] KVM: x86: Do not return host topology information from
KVM_GET_SUPPORTED_CPUID
Passing the host topology to the guest is almost certainly wrong
and will confuse the scheduler. In addition, several fields of
these CPUID leaves vary on each processor; it is simply impossible to
return the right values from KVM_GET_SUPPORTED_CPUID in such a way that
they can be passed to KVM_SET_CPUID2.
The values that will most likely prevent confusion are all zeroes.
Userspace will have to override it anyway if it wishes to present a
specific topology to the guest.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index deb494f759ed..d8ea37dfddf4 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8310,6 +8310,20 @@ CPU[EAX=1]:ECX[24] (TSC_DEADLINE) is not reported by ``KVM_GET_SUPPORTED_CPUID``
It can be enabled if ``KVM_CAP_TSC_DEADLINE_TIMER`` is present and the kernel
has enabled in-kernel emulation of the local APIC.
+CPU topology
+~~~~~~~~~~~~
+
+Several CPUID values include topology information for the host CPU:
+0x0b and 0x1f for Intel systems, 0x8000001e for AMD systems. Different
+versions of KVM return different values for this information and userspace
+should not rely on it. Currently they return all zeroes.
+
+If userspace wishes to set up a guest topology, it should be careful that
+the values of these three leaves differ for each CPU. In particular,
+the APIC ID is found in EDX for all subleaves of 0x0b and 0x1f, and in EAX
+for 0x8000001e; the latter also encodes the core id and node id in bits
+7:0 of EBX and ECX respectively.
+
Obsolete ioctls and capabilities
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b14653b61470..596061c1610e 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -770,16 +770,22 @@ struct kvm_cpuid_array {
int nent;
};
+static struct kvm_cpuid_entry2 *get_next_cpuid(struct kvm_cpuid_array *array)
+{
+ if (array->nent >= array->maxnent)
+ return NULL;
+
+ return &array->entries[array->nent++];
+}
+
static struct kvm_cpuid_entry2 *do_host_cpuid(struct kvm_cpuid_array *array,
u32 function, u32 index)
{
- struct kvm_cpuid_entry2 *entry;
+ struct kvm_cpuid_entry2 *entry = get_next_cpuid(array);
- if (array->nent >= array->maxnent)
+ if (!entry)
return NULL;
- entry = &array->entries[array->nent++];
-
memset(entry, 0, sizeof(*entry));
entry->function = function;
entry->index = index;
@@ -956,22 +962,13 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
entry->edx = edx.full;
break;
}
- /*
- * Per Intel's SDM, the 0x1f is a superset of 0xb,
- * thus they can be handled by common code.
- */
case 0x1f:
case 0xb:
/*
- * Populate entries until the level type (ECX[15:8]) of the
- * previous entry is zero. Note, CPUID EAX.{0x1f,0xb}.0 is
- * the starting entry, filled by the primary do_host_cpuid().
+ * No topology; a valid topology is indicated by the presence
+ * of subleaf 1.
*/
- for (i = 1; entry->ecx & 0xff00; ++i) {
- entry = do_host_cpuid(array, function, i);
- if (!entry)
- goto out;
- }
+ entry->eax = entry->ebx = entry->ecx = 0;
break;
case 0xd: {
u64 permitted_xcr0 = kvm_caps.supported_xcr0 & xstate_get_guest_group_perm();
@@ -1202,6 +1199,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
entry->ebx = entry->ecx = entry->edx = 0;
break;
case 0x8000001e:
+ /* Do not return host topology information. */
+ entry->eax = entry->ebx = entry->ecx = 0;
+ entry->edx = 0; /* reserved */
break;
case 0x8000001F:
if (!kvm_cpu_cap_has(X86_FEATURE_SEV)) {
