linux-kernel - Re: [PATCH v5 2/7] nSVM: introduce smv->nested.save to cache save area fields

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Date:   Thu, 11 Nov 2021 14:52:31 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Emanuele Giuseppe Esposito <eesposit@...hat.com>,
        kvm@...r.kernel.org
Cc:     Maxim Levitsky <mlevitsk@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/7] nSVM: introduce smv->nested.save to cache save
 area fields

On 11/3/21 15:05, Emanuele Giuseppe Esposito wrote:
> Note that in svm_set_nested_state() we want to cache the L2
> save state only if we are in normal non guest mode, because
> otherwise it is not touched.

I think that call to nested_copy_vmcb_save_to_cache is not necessary at 
all, because svm->nested.save is not used afterwards and is not valid 
after VMRUN.

The relevant checks have already been done before:

         if (!(vcpu->arch.efer & EFER_SVME)) {
                 /* GIF=1 and no guest mode are required if SVME=0.  */
                 if (kvm_state->flags != KVM_STATE_NESTED_GIF_SET)
                         return -EINVAL;
         }

	...

         /*
          * Processor state contains L2 state.  Check that it is
          * valid for guest mode (see nested_vmcb_check_save).
          */
         cr0 = kvm_read_cr0(vcpu);
         if (((cr0 & X86_CR0_CD) == 0) && (cr0 & X86_CR0_NW))
                 goto out_free;

(and all other checks are done by KVM_SET_SREGS, KVM_SET_DEBUGREGS etc.)

Paolo