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

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Message-ID: <57c1a18b-b8b0-4368-99b3-b6ad4ad0e614@linux.intel.com>
Date: Sun, 7 Apr 2024 11:47:00 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: isaku.yamahata@...el.com
Cc: 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
Subject: Re: [PATCH v19 080/130] KVM: TDX: restore host xsave state when exit
 from the guest TD



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/

> +		wrmsrl(MSR_IA32_XSS, host_xss);
> +	if (static_cpu_has(X86_FEATURE_PKU) &&
> +	    (kvm_tdx->xfam & XFEATURE_MASK_PKRU))
> +		write_pkru(vcpu->arch.host_pkru);
> +}
> +
>   static noinstr void tdx_vcpu_enter_exit(struct vcpu_tdx *tdx)
>   {
>   	struct tdx_module_args args;
> @@ -609,6 +627,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
>   
>   	tdx_vcpu_enter_exit(tdx);
>   
> +	tdx_restore_host_xsave_state(vcpu);
>   	tdx->host_state_need_restore = true;
>   
>   	vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 23ece956c816..b361d948140f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -315,6 +315,7 @@ const struct kvm_stats_header kvm_vcpu_stats_header = {
>   };
>   
>   u64 __read_mostly host_xcr0;
> +EXPORT_SYMBOL_GPL(host_xcr0);
>   
>   static struct kmem_cache *x86_emulator_cache;
>