linux-kernel - Re: [PATCH] KVM: X86: Fix the decoding of segment overrides in 64bit mode

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Message-ID: <d1126eb9-7203-7044-f72b-174cac6607ab@redhat.com>
Date:   Thu, 22 Mar 2018 11:42:25 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Andrew Cooper <andrew.cooper3@...rix.com>,
        Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH] KVM: X86: Fix the decoding of segment overrides in 64bit
 mode

On 22/03/2018 11:19, Andrew Cooper wrote:
> On 22/03/2018 10:07, Paolo Bonzini wrote:
>> On 22/03/2018 09:34, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpengli@...cent.com>
>>>
>>> Explicit segment overides other than %fs and %gs are documented as ignored by
>>> both Intel and AMD.
>>>
>>> In practice, this means that:
>>>
>>>  * Explicit uses of %ss don't actually yield #SS[0] for non-canonical
>>>    memory references.
>>>  * Explicit uses of %{e,c,d}s don't override %rbp/%rsp-based memory references
>>>    to yield #GP[0] for non-canonical memory references.
>>>
>>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>>> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> 
> When porting fixes from other projects, it is customary to identify so
> in the commit message.  In this case, the fix you've ported is
> http://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=b7dce29d9faf3597d009c853ed1fcbed9f7a7f68
> 
> Here is an example of how Xen ports fixes from Linux for the drivers
> that we share. 
> http://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=4e131596f1defec9407b6e60d584a696beaf5d7e

Thanks Andrew.  The code is of course completely different, but the
commit message is 1:1.  Wanpeng, please acknowledge Jan in v2!

>> Testcase, please...
> 
> If you want to crib from one, this is the testcase I made for Xen.
> 
> http://xenbits.xen.org/docs/xtf/test-memop-seg.html

How does it ensure that the code is executed through the emulator and
not by the processor?

> With the impending KVM/PVH work which is ongoing, it will soon be easy
> to run Xen's HVM test suite unmodified under KVM, but we're not quite
> there yet.

What does the test suite use for console I/O?

Paolo