Re: [PATCH v2 1/5] KVM: nVMX: Advertise support for MSR_IA32_VMX_TRUE_*_CTLS

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Jan Kiszka <jan.kiszka@xxxxxxxxxxx> writes:

> We already implemented them but failed to advertise them. Currently they
> all return the identical values to the capability MSRs they are
> augmenting. So there is no change in exposed features yet.
>
> Drop related comments at this chance that are partially incorrect and
> redundant anyway.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> ---
>  arch/x86/include/uapi/asm/msr-index.h |  1 +
>  arch/x86/kvm/vmx.c                    | 13 ++-----------
>  2 files changed, 3 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/include/uapi/asm/msr-index.h b/arch/x86/include/uapi/asm/msr-index.h
> index fcf2b3a..eaefcc6 100644
> --- a/arch/x86/include/uapi/asm/msr-index.h
> +++ b/arch/x86/include/uapi/asm/msr-index.h
> @@ -558,6 +558,7 @@
>  
>  /* VMX_BASIC bits and bitmasks */
>  #define VMX_BASIC_VMCS_SIZE_SHIFT	32
> +#define VMX_BASIC_TRUE_CTLS		(1ULL << 55)

Curiosity question - know of any case that failed since we didn't
set this bit ?

>  #define VMX_BASIC_64		0x0001000000000000LLU
>  #define VMX_BASIC_MEM_TYPE_SHIFT	50
>  #define VMX_BASIC_MEM_TYPE_MASK	0x003c000000000000LLU
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 801332e..536f341 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2265,21 +2265,13 @@ static __init void nested_vmx_setup_ctls_msrs(void)
>  	/* pin-based controls */
>  	rdmsr(MSR_IA32_VMX_PINBASED_CTLS,
>  	      nested_vmx_pinbased_ctls_low, nested_vmx_pinbased_ctls_high);
> -	/*
> -	 * According to the Intel spec, if bit 55 of VMX_BASIC is off (as it is
> -	 * in our case), bits 1, 2 and 4 (i.e., 0x16) must be 1 in this MSR.
> -	 */
>  	nested_vmx_pinbased_ctls_low |= PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR;
>  	nested_vmx_pinbased_ctls_high &= PIN_BASED_EXT_INTR_MASK |
>  		PIN_BASED_NMI_EXITING | PIN_BASED_VIRTUAL_NMIS;
>  	nested_vmx_pinbased_ctls_high |= PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR |
>  		PIN_BASED_VMX_PREEMPTION_TIMER;
>  
> -	/*
> -	 * Exit controls
> -	 * If bit 55 of VMX_BASIC is off, bits 0-8 and 10, 11, 13, 14, 16 and
> -	 * 17 must be 1.
> -	 */
> +	/* exit controls */
>  	rdmsr(MSR_IA32_VMX_EXIT_CTLS,
>  		nested_vmx_exit_ctls_low, nested_vmx_exit_ctls_high);
>  	nested_vmx_exit_ctls_low = VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR;
> @@ -2299,7 +2291,6 @@ static __init void nested_vmx_setup_ctls_msrs(void)
>  	/* entry controls */
>  	rdmsr(MSR_IA32_VMX_ENTRY_CTLS,
>  		nested_vmx_entry_ctls_low, nested_vmx_entry_ctls_high);
> -	/* If bit 55 of VMX_BASIC is off, bits 0-8 and 12 must be 1. */
>  	nested_vmx_entry_ctls_low = VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR;
>  	nested_vmx_entry_ctls_high &=
>  #ifdef CONFIG_X86_64
> @@ -2394,7 +2385,7 @@ static int vmx_get_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
>  		 * guest, and the VMCS structure we give it - not about the
>  		 * VMX support of the underlying hardware.
>  		 */
> -		*pdata = VMCS12_REVISION |
> +		*pdata = VMCS12_REVISION | VMX_BASIC_TRUE_CTLS |
>  			   ((u64)VMCS12_SIZE << VMX_BASIC_VMCS_SIZE_SHIFT) |
>  			   (VMX_BASIC_MEM_TYPE_WB << VMX_BASIC_MEM_TYPE_SHIFT);
>  		break;
--
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