Re: [PATCH] KMV: VMX: consult IA32_VMX_EPT_VPID_CAP to determine EPT paging-structure memory type

[Sheng Yang <sheng@linux.intel.com>]

On Monday 22 March 2010 17:06:42 Gui Jianfeng wrote:
> According to SDM, we need to configure EPT paging-structure memory type
> by consulting IA32_VMX_EPT_VPID_CAP.
> 
> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
> ---
>  arch/x86/include/asm/vmx.h |    2 ++
>  arch/x86/kvm/vmx.c         |   12 +++++++++---
>  2 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index fb9a080..1b33a60 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -374,6 +374,8 @@ enum vmcs_field {
>  #define VMX_EPT_MT_EPTE_SHIFT			3
>  #define VMX_EPT_GAW_EPTP_SHIFT			3
>  #define VMX_EPT_DEFAULT_MT			0x6ull
> +#define VMX_EPT_MT_WRBACK			0x6ull
> +#define VMX_EPT_MT_UNCACHABLE			0x0ull
>  #define VMX_EPT_READABLE_MASK			0x1ull
>  #define VMX_EPT_WRITABLE_MASK			0x2ull
>  #define VMX_EPT_EXECUTABLE_MASK			0x4ull
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 06108f3..f971b9b 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1804,9 +1804,15 @@ static u64 construct_eptp(unsigned long root_hpa)
>  {
>  	u64 eptp;
> 
> -	/* TODO write the value reading from MSR */
> -	eptp = VMX_EPT_DEFAULT_MT |
> -		VMX_EPT_DEFAULT_GAW << VMX_EPT_GAW_EPTP_SHIFT;
> +	if (cpu_has_vmx_eptp_writeback())
> +		eptp = VMX_EPT_MT_WRBACK |
> +			VMX_EPT_DEFAULT_GAW << VMX_EPT_GAW_EPTP_SHIFT;

I prefer to ensure WB is supported and used as default. Otherwise it would be 
a big trouble for memory subsystem(to use UC for all memory). Both WB and UC 
EPT memory types are ensured to be support in hardware.

And you can remove VMX_EPT_DEFAULT_MT as well.

-- 
regards
Yang, Sheng

> +	else if (cpu_has_vmx_eptp_uncacheable())
> +		eptp = VMX_EPT_MT_UNCACHABLE |
> +			VMX_EPT_DEFAULT_GAW << VMX_EPT_GAW_EPTP_SHIFT;
> +	else
> +		BUG();
> +
>  	eptp |= (root_hpa & PAGE_MASK);
> 
>  	return eptp;
>