diff mbox series

[v2,1/7] hyperv: Detect Nested virtualization support for SVM

Message ID 9d12558549bc0c6f179b26f5b16c751bdfab3f74.1618492553.git.viremana@linux.microsoft.com (mailing list archive)
State New
Headers show
Series Hyper-V nested virt enlightenments for SVM | expand

Commit Message

Vineeth Pillai April 15, 2021, 1:43 p.m. UTC
Detect nested features exposed by Hyper-V if SVM is enabled.

Signed-off-by: Vineeth Pillai <viremana@linux.microsoft.com>
---
 arch/x86/kernel/cpu/mshyperv.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Comments

Vitaly Kuznetsov April 16, 2021, 8:26 a.m. UTC | #1
Vineeth Pillai <viremana@linux.microsoft.com> writes:

> Detect nested features exposed by Hyper-V if SVM is enabled.
>

It may make sense to expand this a bit as it is probably unclear how the
change is related to SVM.

Something like:

HYPERV_CPUID_NESTED_FEATURES CPUID leaf can be present on both Intel and
AMD Hyper-V guests. Previously, the code was using
HV_X64_ENLIGHTENED_VMCS_RECOMMENDED feature bit to determine the
availability of nested features leaf and this complies to TLFS:
"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 detection method doesn't work for AMD. Use
HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS.EAX CPUID information ("The
maximum input value for hypervisor CPUID information.") instead, this
works for both AMD and Intel.


> Signed-off-by: Vineeth Pillai <viremana@linux.microsoft.com>
> ---
>  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 3546d3e21787..c6f812851e37 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",
> +			ms_hyperv.nested_features);
>  	}
>  
>  	/*

With the commit message expanded,

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Vineeth Pillai April 16, 2021, 4:10 p.m. UTC | #2
> It may make sense to expand this a bit as it is probably unclear how the
> change is related to SVM.
>
> Something like:
>
> HYPERV_CPUID_NESTED_FEATURES CPUID leaf can be present on both Intel and
> AMD Hyper-V guests. Previously, the code was using
> HV_X64_ENLIGHTENED_VMCS_RECOMMENDED feature bit to determine the
> availability of nested features leaf and this complies to TLFS:
> "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 detection method doesn't work for AMD. Use
> HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS.EAX CPUID information ("The
> maximum input value for hypervisor CPUID information.") instead, this
> works for both AMD and Intel.
Thanks for the input. Will update the commit message in next revision.

Thanks,
Vineeth
diff mbox series

Patch

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 3546d3e21787..c6f812851e37 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",
+			ms_hyperv.nested_features);
 	}
 
 	/*