Re: [Xen-devel] [PATCH RFC 05/14] xen: vmx: Disable the 2M/1G superpage when SPP enabled

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Fri, Oct 20, 2017 at 2:44 AM, Yi Zhang <yi.z.zhang@xxxxxxxxxxxxxxx> wrote:
> On 2017-10-19 at 12:17:12 -0600, Tamas K Lengyel wrote:
>> On Thu, Oct 19, 2017 at 2:11 AM, Zhang Yi <yi.z.zhang@xxxxxxxxxxxxxxx> wrote:
>> > From: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
>> >
>> > Current we only support Sub-page Protection on the 4k
>> > page table.
>> >
>> > Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
>> > ---
>> >  xen/arch/x86/hvm/vmx/vmx.c | 6 ++++++
>> >  1 file changed, 6 insertions(+)
>> >
>> > diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
>> > index 04ae0d6..a4c24bb 100644
>> > --- a/xen/arch/x86/hvm/vmx/vmx.c
>> > +++ b/xen/arch/x86/hvm/vmx/vmx.c
>> > @@ -2497,6 +2497,12 @@ const struct hvm_function_table * __init 
>> > start_vmx(void)
>> >          vmx_function_table.get_guest_bndcfgs = vmx_get_guest_bndcfgs;
>> >      }
>> >
>> > +    if ( cpu_has_vmx_ept_spp )
>>
>> I think this really only ought to happen if the command-line option
>> has also been enabled.
>
> Sorry, didn't catch your point, the command line option opt_hap_2m and
> opt_hap_1G was enable by default, I need to  disable the supper page
> when spp feature enabled. Did you mean that if we enable 2M/1G by
> command-line we couldn't disable it here? yes, it is, I will improve
> this logic. Thank you Tamas.

I meant that right now "cpu_has_vmx_ept_spp" looks like just checks
whether the CPU supports SPP, not whether the command-line option was
set to enable it. If the command line option is not set (or
specifically disables SPP) then the large pages shouldn't get
disabled.

>
>>
>> > +    {
>> > +        vmx_function_table.hap_capabilities &= ~HVM_HAP_SUPERPAGE_2MB;
>> > +        vmx_function_table.hap_capabilities &= ~HVM_HAP_SUPERPAGE_1GB;
>> > +    }
>> > +
>> >      setup_vmcs_dump();
>> >
>> >      lbr_tsx_fixup_check();
>> > --
>> > 2.7.4

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