linux-kernel - Re: [PATCH] KVM: nVMX: VMX instructions: fix segment checks when L1 is in long mode.

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Message-ID: <24080992-801c-4606-c801-65ee68cf8779@redhat.com>
Date:	Thu, 23 Jun 2016 18:03:01 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Quentin Casasnovas <quentin.casasnovas@...cle.com>,
	x86 <x86@...nel.org>, kvm <kvm@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Cc:	Eugene Korenevsky <ekorenevsky@...il.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	linux-stable <stable@...r.kernel.org>
Subject: Re: [PATCH] KVM: nVMX: VMX instructions: fix segment checks when L1
 is in long mode.



On 18/06/2016 11:01, Quentin Casasnovas wrote:
> Cross-checking the KVM/VMX VMREAD emulation code with the Intel Software
> Developper Manual Volume 3C - "VMREAD - Read Field from Virtual-Machine
> Control Structure", I found that we're enforcing that the destination
> operand is NOT located in a read-only data segment or any code segment when
> the L1 is in long mode - BUT that check should only happen when it is in
> protected mode.
> 
> Shuffling the code a bit to make our emulation follow the specification
> allows me to boot a Xen dom0 in a nested KVM and start HVM L2 guests
> without problems.

That's great, and I'm applying the patch, but it's also pretty weird. :)
 Do you have a pointer to Xen source code that does a VMREAD into a
read-only data segment or a code segment?

Thanks,

Paolo