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

From: Yi Zhang <yi.z.zhang@linux.intel.com>
To: Tamas K Lengyel <tamas@tklengyel.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
	"wei.liu2@citrix.com" <wei.liu2@citrix.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Razvan Cojocaru <rcojocaru@bitdefender.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH RFC 05/14] xen: vmx: Disable the 2M/1G superpage when SPP enabled
Date: Wed, 25 Oct 2017 23:32:21 +0800	[thread overview]
Message-ID: <20171025153220.GA8038@dazhang1-ssd.sh.intel.com> (raw)
In-Reply-To: <CABfawh=54dasasGD0Ob8c=08=YwVEuo9eTVL7Sz3hr-9XKo_aA@mail.gmail.com>

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@linux.intel.com> 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@linux.intel.com> wrote:
> >> > From: Zhang Yi Z <yi.z.zhang@linux.intel.com>
> >> >
> >> > Current we only support Sub-page Protection on the 4k
> >> > page table.
> >> >
> >> > Signed-off-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
> >> > ---
> >> >  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"

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