linux-kernel - Re: [PATCH V2 07/12] KVM: TDX: restore host xsave state when exit from the guest TD

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Message-ID: <c7368616-063a-44c1-81d4-12ee903c2072@intel.com>
Date: Fri, 28 Feb 2025 09:58:44 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Adrian Hunter <adrian.hunter@...el.com>, pbonzini@...hat.com,
 seanjc@...gle.com
Cc: kvm@...r.kernel.org, rick.p.edgecombe@...el.com, kai.huang@...el.com,
 reinette.chatre@...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, yan.y.zhao@...el.com,
 chao.gao@...el.com, weijiang.yang@...el.com
Subject: Re: [PATCH V2 07/12] KVM: TDX: restore host xsave state when exit
 from the guest TD

On 2/27/2025 10:29 PM, Adrian Hunter wrote:
>>>    +    vcpu->arch.cr4 = ~vcpu->arch.cr4_guest_rsvd_bits;
>> when userspace doesn't configure XFEATURE_MASK_PKRU in XFAM, it seems kvm_load_host_xsave_state() will skip restore host's PKRU value.
> That's correct.

FYI, in this case, it's safe and functional though 
kvm_load_host_xsave_state() skips restoring the host's PKRU value.
Because host's PKRU is not clobbered after TD exit when XFAM.PKU is 0. 
So no need to restore.