linux-kernel - Re: [PATCH 4/7] KVM: TDX: restore host xsave state when exit from the guest TD

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Message-ID: <87125f6d-8912-41ad-b01f-f6e68f8a6a89@intel.com>
Date: Mon, 25 Nov 2024 13:34:48 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Chao Gao <chao.gao@...el.com>
Cc: pbonzini@...hat.com, seanjc@...gle.com, kvm@...r.kernel.org,
 dave.hansen@...ux.intel.com, rick.p.edgecombe@...el.com,
 kai.huang@...el.com, reinette.chatre@...el.com, xiaoyao.li@...el.com,
 tony.lindgren@...ux.intel.com, binbin.wu@...ux.intel.com,
 dmatlack@...gle.com, isaku.yamahata@...el.com, nik.borisov@...e.com,
 linux-kernel@...r.kernel.org, x86@...nel.org, yan.y.zhao@...el.com,
 weijiang.yang@...el.com
Subject: Re: [PATCH 4/7] KVM: TDX: restore host xsave state when exit from the
 guest TD

On 22/11/24 07:49, Chao Gao wrote:
>> +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) &&
>> +	    kvm_host.xcr0 != (kvm_tdx->xfam & kvm_caps.supported_xcr0))
>> +		xsetbv(XCR_XFEATURE_ENABLED_MASK, kvm_host.xcr0);
>> +	if (static_cpu_has(X86_FEATURE_XSAVES) &&
>> +	    /* PT can be exposed to TD guest regardless of KVM's XSS support */
>> +	    kvm_host.xss != (kvm_tdx->xfam &
>> +			 (kvm_caps.supported_xss | XFEATURE_MASK_PT |
>> +			  XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL)))
> 
> Should we drop CET/PT from this series? I think they are worth a new
> patch/series.
> 
>> +		wrmsrl(MSR_IA32_XSS, kvm_host.xss);
>> +	if (static_cpu_has(X86_FEATURE_PKU) &&
> 
> How about using cpu_feature_enabled()? It is used in kvm_load_host_xsave_state()
> It handles the case where CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS is not
> enabled.

Seems reasonable

> 
>> +	    (kvm_tdx->xfam & XFEATURE_MASK_PKRU))
>> +		write_pkru(vcpu->arch.host_pkru);
> 
> If host_pkru happens to match the hardware value after TD-exits, the write can
> be omitted, similar to what is done above for xss and xcr0.
> 
>> +}