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

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Wed, Oct 25, 2017 at 9:32 AM, Yi Zhang <yi.z.zhang@xxxxxxxxxxxxxxx> wrote:
> On 2017-10-24 at 11:43:45 -0600, Tamas K Lengyel wrote:
>> 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.
>>
>
> In patch 02/14, if we didn't set spp_enable, we will not set the spp cap
> in vmx_secondary_exec_control, so cp_has_vmx_ept_spp flag will set when
> hardware has spp cap and xen cmdlline passed the parameter "spp_enable=1"

OK, thanks, I missed that.

>
>> >
>> >>
>> >> > +    {
>> >> > +        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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