From: Vineeth Pillai <viremana@xxxxxxxxxxxxxxxxxxx> Sent: Thursday, June 3, 2021 8:15 AM
>
> Previously, to detect nested virtualization enlightenment support,
> we were using HV_X64_ENLIGHTENED_VMCS_RECOMMENDED feature bit of
> HYPERV_CPUID_ENLIGHTMENT_INFO.EAX CPUID as docuemented in TLFS:
s/docuemented/documented/
> "Bit 14: Recommend a nested hypervisor using the enlightened VMCS
> interface. Also indicates that additional nested enlightenments
> may be available (see leaf 0x4000000A)".
>
> Enlightened VMCS, however, is an Intel only feature so the above
> detection method doesn't work for AMD. So, use the
> HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS.EAX CPUID information ("The
> maximum input value for hypervisor CPUID information.") and this
> works for both AMD and Intel.
>
> Signed-off-by: Vineeth Pillai <viremana@xxxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kernel/cpu/mshyperv.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 22f13343b5da..c268c2730048 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -252,6 +252,7 @@ static void __init hv_smp_prepare_cpus(unsigned int max_cpus)
>
> static void __init ms_hyperv_init_platform(void)
> {
> + int hv_max_functions_eax;
> int hv_host_info_eax;
> int hv_host_info_ebx;
> int hv_host_info_ecx;
> @@ -269,6 +270,8 @@ static void __init ms_hyperv_init_platform(void)
> ms_hyperv.misc_features = cpuid_edx(HYPERV_CPUID_FEATURES);
> ms_hyperv.hints = cpuid_eax(HYPERV_CPUID_ENLIGHTMENT_INFO);
>
> + hv_max_functions_eax =
> cpuid_eax(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS);
> +
> pr_info("Hyper-V: privilege flags low 0x%x, high 0x%x, hints 0x%x, misc 0x%x\n",
> ms_hyperv.features, ms_hyperv.priv_high, ms_hyperv.hints,
> ms_hyperv.misc_features);
> @@ -298,8 +301,7 @@ static void __init ms_hyperv_init_platform(void)
> /*
> * Extract host information.
> */
> - if (cpuid_eax(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS) >=
> - HYPERV_CPUID_VERSION) {
> + if (hv_max_functions_eax >= HYPERV_CPUID_VERSION) {
> hv_host_info_eax = cpuid_eax(HYPERV_CPUID_VERSION);
> hv_host_info_ebx = cpuid_ebx(HYPERV_CPUID_VERSION);
> hv_host_info_ecx = cpuid_ecx(HYPERV_CPUID_VERSION);
> @@ -325,9 +327,11 @@ static void __init ms_hyperv_init_platform(void)
> ms_hyperv.isolation_config_a, ms_hyperv.isolation_config_b);
> }
>
> - if (ms_hyperv.hints & HV_X64_ENLIGHTENED_VMCS_RECOMMENDED) {
> + if (hv_max_functions_eax >= HYPERV_CPUID_NESTED_FEATURES) {
> ms_hyperv.nested_features =
> cpuid_eax(HYPERV_CPUID_NESTED_FEATURES);
> + pr_info("Hyper-V: Nested features: 0x%x\n",
Nit: Drop the colon after "Nested features". Current code isn't very consistent
but I'm trying to establish the pattern of "Hyper-V:" followed by names and
values, with multiple name/value pairs separated by a comma.
> + ms_hyperv.nested_features);
> }
>
> /*
> --
> 2.25.1
Nits notwithstanding,
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
