linux-kernel - Re: [PATCH v3 7/8] KVM: x86: Introduce KVM_GET_SREGS2 / KVM_SET

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Date:   Thu, 10 Jun 2021 17:06:04 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     open list <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Jim Mattson <jmattson@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3 7/8] KVM: x86: Introduce KVM_GET_SREGS2 /
 KVM_SET_SREGS2

On 07/06/21 11:02, Maxim Levitsky wrote:
> +static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2)
> +{
> +	int mmu_reset_needed = 0;
> +	bool valid_pdptrs = sregs2->flags & KVM_SREGS2_FLAGS_PDPTRS_VALID;
> +	int i, ret;
>   
> +	if (sregs2->flags & ~KVM_SREGS2_FLAGS_PDPTRS_VALID)
> +		return -EINVAL;
> +
> +	ret = __set_sregs_common(vcpu, (struct kvm_sregs *)sregs2,
> +				 &mmu_reset_needed, !valid_pdptrs);
> +	if (ret)
> +		return ret;
> +
> +	if (valid_pdptrs) {
> +		if (!is_pae_paging(vcpu))
> +			return -EINVAL;
> +		if (vcpu->arch.guest_state_protected)
> +			return -EINVAL;
> +		for (i = 0 ; i < 4 ; i++)
> +			kvm_pdptr_write(vcpu, i, sregs2->pdptrs[i]);
> +
> +		kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
> +		mmu_reset_needed = 1;
> +	}
> +	if (mmu_reset_needed)
> +		kvm_mmu_reset_context(vcpu);
> +	return 0;
>   }

It's a bit nicer if the checks are done early:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f20c7c06bd4a..c6f8fec78c53 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10248,22 +10248,23 @@ static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2)
  {
         int mmu_reset_needed = 0;
         bool valid_pdptrs = sregs2->flags & KVM_SREGS2_FLAGS_PDPTRS_VALID;
+       bool pae = (sregs2->cr0 & X86_CR0_PG) && (sregs2->cr4 & X86_CR4_PAE) &&
+               !(sregs2->efer & EFER_LMA);
         int i, ret;
  
         if (sregs2->flags & ~KVM_SREGS2_FLAGS_PDPTRS_VALID)
                 return -EINVAL;
  
+       if (valid_pdptrs && (!pae || vcpu->arch.guest_state_protected))
+               return -EINVAL;
+
         ret = __set_sregs_common(vcpu, (struct kvm_sregs *)sregs2,
                                  &mmu_reset_needed, !valid_pdptrs);
         if (ret)
                 return ret;
  
         if (valid_pdptrs) {
-               if (!is_pae_paging(vcpu))
-                       return -EINVAL;
-               if (vcpu->arch.guest_state_protected)
-                       return -EINVAL;
-               for (i = 0 ; i < 4 ; i++)
+               for (i = 0; i < 4 ; i++)
                         kvm_pdptr_write(vcpu, i, sregs2->pdptrs[i]);
  
                 kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);

Paolo