linux-kernel - Re: [PATCH v19 080/130] KVM: TDX: restore host xsave state when exit from the guest TD

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Date: Fri, 12 Apr 2024 13:19:00 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 080/130] KVM: TDX: restore host xsave state when exit
 from the guest TD

On Sun, Apr 07, 2024 at 11:47:00AM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> 
> On 2/26/2024 4:26 PM, isaku.yamahata@...el.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > 
> > On exiting from the guest TD, xsave state is clobbered.  Restore xsave
> > state on TD exit.
> > 
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> > v19:
> > - Add EXPORT_SYMBOL_GPL(host_xcr0)
> > 
> > v15 -> v16:
> > - Added CET flag mask
> > 
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> >   arch/x86/kvm/vmx/tdx.c | 19 +++++++++++++++++++
> >   arch/x86/kvm/x86.c     |  1 +
> >   2 files changed, 20 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 9616b1aab6ce..199226c6cf55 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -2,6 +2,7 @@
> >   #include <linux/cpu.h>
> >   #include <linux/mmu_context.h>
> > +#include <asm/fpu/xcr.h>
> >   #include <asm/tdx.h>
> >   #include "capabilities.h"
> > @@ -534,6 +535,23 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> >   	 */
> >   }
> > +static void tdx_restore_host_xsave_state(struct kvm_vcpu *vcpu)
> > +{
> > +	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
> > +
> > +	if (static_cpu_has(X86_FEATURE_XSAVE) &&
> > +	    host_xcr0 != (kvm_tdx->xfam & kvm_caps.supported_xcr0))
> > +		xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
> > +	if (static_cpu_has(X86_FEATURE_XSAVES) &&
> > +	    /* PT can be exposed to TD guest regardless of KVM's XSS support */
> The comment needs to be updated to reflect the case for CET.
> 
> > +	    host_xss != (kvm_tdx->xfam &
> > +			 (kvm_caps.supported_xss | XFEATURE_MASK_PT | TDX_TD_XFAM_CET)))
> 
> For TDX_TD_XFAM_CET, maybe no need to make it TDX specific?
> 
> BTW, the definitions for XFEATURE_MASK_CET_USER/XFEATURE_MASK_CET_KERNEL
> have been merged.
> https://lore.kernel.org/all/20230613001108.3040476-25-rick.p.edgecombe%40intel.com
> You can resolve the TODO in https://lore.kernel.org/kvm/5eca97e6a3978cf4dcf1cff21be6ec8b639a66b9.1708933498.git.isaku.yamahata@intel.com/

Yes, will update those constants to use the one in arch/x86/include/asm/fpu/types.h
-- 
Isaku Yamahata <isaku.yamahata@...el.com>