From: Paolo Bonzini pbonzini@redhat.com
[ Upstream commit 45e966fcca03ecdcccac7cb236e16eea38cc18af ]
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@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- Documentation/virt/kvm/api.rst | 14 ++++++++++++++ arch/x86/kvm/cpuid.c | 32 ++++++++++++++++---------------- 2 files changed, 30 insertions(+), 16 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index d807994360d4..2b4b64797191 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6433,6 +6433,20 @@ 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 06a776fdb90c..de4b171cb76b 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -511,16 +511,22 @@ 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++]; - entry->function = function; entry->index = index; entry->flags = 0; @@ -698,22 +704,13 @@ 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: entry->eax &= supported_xcr0; @@ -866,6 +863,9 @@ 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; /* Support memory encryption cpuid if host supports it */ case 0x8000001F: