linux-kernel - Re: [PATCH] kvm: x86: fix RSM when PCID is non-zero

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Message-ID: <CALCETrVa6DxfQNZMqryHf_tD06QwXT79nbPa=yS2GJBHQybKrA@mail.gmail.com>
Date:   Thu, 21 Dec 2017 07:30:35 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm list <kvm@...r.kernel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Laszlo Ersek <lersek@...hat.com>
Subject: Re: [PATCH] kvm: x86: fix RSM when PCID is non-zero

On Thu, Dec 21, 2017 at 3:56 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> rsm_load_state_64() and rsm_enter_protected_mode() load CR3, then
> CR4 & ~PCIDE, then CR0, then CR4.
>
> However, setting CR4.PCIDE fails if CR3[11:0] != 0.  It's probably easier
> in the long run to replace rsm_enter_protected_mode() with an emulator
> callback that sets all the special registers (like KVM_SET_SREGS would
> do).  For now, set the PCID field of CR3 only after CR4.PCIDE is 1.

Out of curiosity, has anyone ever tested RSM returning to PAE mode?  I
*think* it's supposed to restore the PDPTR registers directly rather
than reloading them from the memory pointed to by CR3, and it doesn't
look like the new or old code does it.

--Andy