linux-kernel - Re: [PATCH v3 2/3] KVM: x86: Move pkru save/restore to x86.c

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Message-ID: <6982aaa9-d1ee-db8a-2eeb-6063c9bc342c@redhat.com>
Date:   Wed, 13 May 2020 08:47:07 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Babu Moger <babu.moger@....com>, Jim Mattson <jmattson@...gle.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        mchehab+samsung@...nel.org, changbin.du@...el.com,
        Nadav Amit <namit@...are.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        yang.shi@...ux.alibaba.com,
        Anthony Steinhauser <asteinhauser@...gle.com>,
        anshuman.khandual@....com, Jan Kiszka <jan.kiszka@...mens.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        steven.price@....com, rppt@...ux.vnet.ibm.com, peterx@...hat.com,
        Dan Williams <dan.j.williams@...el.com>,
        Arjun Roy <arjunroy@...gle.com>, logang@...tatee.com,
        Thomas Hellstrom <thellstrom@...are.com>,
        Andrea Arcangeli <aarcange@...hat.com>, justin.he@....com,
        robin.murphy@....com, ira.weiny@...el.com,
        Kees Cook <keescook@...omium.org>,
        Juergen Gross <jgross@...e.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        pawan.kumar.gupta@...ux.intel.com,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        vineela.tummalapalli@...el.com, yamada.masahiro@...ionext.com,
        sam@...nborg.org, acme@...hat.com, linux-doc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 2/3] KVM: x86: Move pkru save/restore to x86.c

On 12/05/20 19:17, Babu Moger wrote:
> 
> On 5/12/20 11:39 AM, Jim Mattson wrote:
>> On Mon, May 11, 2020 at 4:33 PM Babu Moger <babu.moger@....com> wrote:
>>> MPK feature is supported by both VMX and SVM. So we can
>>> safely move pkru state save/restore to common code. Also
>>> move all the pkru data structure to kvm_vcpu_arch.
>>>
>>> Also fixes the problem Jim Mattson pointed and suggested below.
>>>
>>> "Though rdpkru and wrpkru are contingent upon CR4.PKE, the PKRU
>>> resource isn't. It can be read with XSAVE and written with XRSTOR.
>>> So, if we don't set the guest PKRU value here(kvm_load_guest_xsave_state),
>>> the guest can read the host value.
>>>
>>> In case of kvm_load_host_xsave_state, guest with CR4.PKE clear could
>>> potentially use XRSTOR to change the host PKRU value"
>>>
>>> Signed-off-by: Babu Moger <babu.moger@....com>
>> I would do the bugfix as a separate commit, to ease backporting it to
>> the stable branches.
> Ok. Sure.

I will take care of this for v4 (pick this patch up and put it in
5.7-rc, package everything as a topic branch, merge it to kvm/next).

Paolo