Re: [PATCH v11 2/7] x86/kvm/hyper-v: Simplify addition for custom cpuid leafs
From: Roman Kagan <hidden>
Date: 2020-05-13 09:24:13
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kvm
On Fri, Apr 24, 2020 at 02:37:41PM +0300, Jon Doron wrote:
Simlify the code to define a new cpuid leaf group by enabled feature. This also fixes a bug in which the max cpuid leaf was always set to HYPERV_CPUID_NESTED_FEATURES regardless if nesting is supported or not.
I'm not sure the bug is there. My understanding is that HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS is supposed to provide the range of leaves that return meaningful information. HYPERV_CPUID_NESTED_FEATURES *can* return meaningful information regardless of whether nested virt is active. So I'd rather skip reducing the returned set if !evmcs_ver. The returned set is sparse in .function anyway; anything that isn't there will just return zeros to the guest. Changing the cpuid is also guest-visible so care must be taken with this.
Any new CPUID group needs to consider the max leaf and be added in the correct order, in this method there are two rules: 1. Each cpuid leaf group must be order in an ascending order 2. The appending for the cpuid leafs by features also needs to happen by ascending order.
It looks like unnecessary complication. I think all you need to do to simplify adding new leaves is to add a macro to hyperv-tlfs.h, say, HYPERV_CPUID_MAX_PRESENT_LEAF, define it to HYPERV_CPUID_NESTED_FEATURES, and redefine once another leaf is added (compat may need to be taken care of). Thanks, Roman.
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Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Jon Doron <redacted> --- arch/x86/kvm/hyperv.c | 46 ++++++++++++++++++++++++++++++------------- 1 file changed, 32 insertions(+), 14 deletions(-)diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index bcefa9d4e57e..ab3e9dbcabbe 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c@@ -1785,27 +1785,45 @@ int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args) return kvm_hv_eventfd_assign(kvm, args->conn_id, args->fd); } +/* Must be sorted in ascending order by function */ +static struct kvm_cpuid_entry2 core_cpuid_entries[] = { + { .function = HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS }, + { .function = HYPERV_CPUID_INTERFACE }, + { .function = HYPERV_CPUID_VERSION }, + { .function = HYPERV_CPUID_FEATURES }, + { .function = HYPERV_CPUID_ENLIGHTMENT_INFO }, + { .function = HYPERV_CPUID_IMPLEMENT_LIMITS }, +}; + +static struct kvm_cpuid_entry2 evmcs_cpuid_entries[] = { + { .function = HYPERV_CPUID_NESTED_FEATURES }, +}; + +#define HV_MAX_CPUID_ENTRIES \ + (ARRAY_SIZE(core_cpuid_entries) +\ + ARRAY_SIZE(evmcs_cpuid_entries)) + int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid, struct kvm_cpuid_entry2 __user *entries) { uint16_t evmcs_ver = 0; - struct kvm_cpuid_entry2 cpuid_entries[] = { - { .function = HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS }, - { .function = HYPERV_CPUID_INTERFACE }, - { .function = HYPERV_CPUID_VERSION }, - { .function = HYPERV_CPUID_FEATURES }, - { .function = HYPERV_CPUID_ENLIGHTMENT_INFO }, - { .function = HYPERV_CPUID_IMPLEMENT_LIMITS }, - { .function = HYPERV_CPUID_NESTED_FEATURES }, - }; - int i, nent = ARRAY_SIZE(cpuid_entries); + struct kvm_cpuid_entry2 cpuid_entries[HV_MAX_CPUID_ENTRIES]; + int i, nent = 0; + + /* Set the core cpuid entries required for Hyper-V */ + memcpy(&cpuid_entries[nent], &core_cpuid_entries, + sizeof(core_cpuid_entries)); + nent = ARRAY_SIZE(core_cpuid_entries); if (kvm_x86_ops.nested_get_evmcs_version) evmcs_ver = kvm_x86_ops.nested_get_evmcs_version(vcpu); - /* Skip NESTED_FEATURES if eVMCS is not supported */ - if (!evmcs_ver) - --nent; + if (evmcs_ver) { + /* EVMCS is enabled, add the required EVMCS CPUID leafs */ + memcpy(&cpuid_entries[nent], &evmcs_cpuid_entries, + sizeof(evmcs_cpuid_entries)); + nent += ARRAY_SIZE(evmcs_cpuid_entries); + } if (cpuid->nent < nent) return -E2BIG;@@ -1821,7 +1839,7 @@ int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid, case HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS: memcpy(signature, "Linux KVM Hv", 12); - ent->eax = HYPERV_CPUID_NESTED_FEATURES; + ent->eax = cpuid_entries[nent - 1].function; ent->ebx = signature[0]; ent->ecx = signature[1]; ent->edx = signature[2];-- 2.24.1