Re: [Xen-devel] [PATCH v2 7/8] x86/vvmx: correctly report vvmcs size

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Nov 08, 2018 at 10:28:24AM +0000, Sergey Dyasli wrote:
> On 07/11/2018 13:28, Wei Liu wrote:
> > On Tue, Nov 06, 2018 at 12:07:58PM +0000, Sergey Dyasli wrote:
> >> The size of Xen's virtual vmcs region is 4096 bytes (see comment about
> >> Virtual VMCS layout in include/asm-x86/hvm/vmx/vvmx.h). Correctly report
> >> it to the guest in case when VMCS shadowing is not available instead of
> >> providing H/W value (which is usually smaller).
> >>
> >> Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
> >> ---
> >> v2:
> >> - slight commit message change
> >> ---
> >>  xen/arch/x86/hvm/vmx/vvmx.c | 8 ++++++++
> >>  1 file changed, 8 insertions(+)
> >>
> >> diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
> >> index 2f5370ceed..37d3cdd859 100644
> >> --- a/xen/arch/x86/hvm/vmx/vvmx.c
> >> +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> >> @@ -2101,6 +2101,14 @@ int nvmx_msr_read_intercept(unsigned int msr, u64 
> >> *msr_content)
> >>          data = (host_data & (~0ul << 32)) |
> >>                 (vmcs->vmcs_revision_id & 0x7fffffff);
> >>          unmap_domain_page(vmcs);
> >> +
> >> +        if ( !cpu_has_vmx_vmcs_shadowing )
> >> +        {
> >> +            /* Report vmcs_region_size as 4096 */
> >> +            data &= ~VMX_BASIC_VMCS_SIZE_MASK;
> >> +            data |= 1ULL << 44;
> > 
> > Can you introduce a define for this to avoid using a magic number?
> 
> I don't see much point in making a define for several reasons:
> 
> 1. It's not going to be used anywhere else
> 
> 2. Intel SDM clearly states that VMCS size is "at most 4096 (bit 44
>    is set if and only if bits 43:32 are clear)"
> 
> 3. My VMX MSRs series will introduce a nice struct, after which this
>    assignment will look like "basic.vmcs_region_size = 4096;"
> 

Fair enough. I have no objection anymore.

Wei.

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