Re: [PATCH v2 4/6] KVM: x86: Introduce KVM_GET_SREGS2 / KVM_SET_SREGS2

From: Paolo Bonzini <pbonzini@redhat.com>
To: Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc: "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Jonathan Corbet <corbet@lwn.net>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@vger.kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Wanpeng Li <wanpengli@tencent.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Jim Mattson <jmattson@google.com>,
	Sean Christopherson <seanjc@google.com>,
	Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH v2 4/6] KVM: x86: Introduce KVM_GET_SREGS2 / KVM_SET_SREGS2
Date: Mon, 26 Apr 2021 14:32:26 +0200	[thread overview]
Message-ID: <898a9b18-4578-cb9d-ece7-f45ba5b7bb89@redhat.com> (raw)
In-Reply-To: <20210426111333.967729-5-mlevitsk@redhat.com>

On 26/04/21 13:13, Maxim Levitsky wrote:
> +	if (sregs2->flags & KVM_SREGS2_FLAGS_PDPTRS_VALID) {
> +
> +		if (!is_pae_paging(vcpu))
> +			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;
> +	}

I think this should also have

	else {
		if (is_pae_paging(vcpu))
			return -EINVAL;
	}

but perhaps even better, check it at the beginning:

	if ((sregs->cr4 & X86_CR4_PAE) &&
             !!(sregs->efer & EFER_LMA) == !!(sregs2->flags & KVM_SREGS2_FLAGS_PDPTRS_VALID))
		return -EINVAL;

which technically means the flag is redundant, but there is some value in
having the flag and not allowing the user to shoot itself in the foot.

Paolo