From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Jim Mattson <jmattson@google.com>,
Steve Rutherford <srutherford@google.com>,
kvm@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>,
Prasad Pandit <ppandit@redhat.com>,
kernellwp@gmail.com
Subject: Re: [PATCH] KVM: x86: Introduce segmented_write_std
Date: Fri, 20 Jan 2017 18:57:47 +0100 [thread overview]
Message-ID: <20170120175746.GE6291@potion> (raw)
In-Reply-To: <96b2e3ff-8566-a0b8-3302-3ee6a44ab5bf@redhat.com>
2017-01-20 18:09+0100, Paolo Bonzini:
> On 20/01/2017 17:55, Jim Mattson wrote:
>> Why attempt to emulate these instructions at all, if we're not going
>> to handle a data access to emulated/special memory?
>>
>> It seems that one of the following three cases must hold:
>>
>> 1) The data accessed by the instruction is emulated/special memory.
>> 2) The instruction was fetched from emulated/special memory.
>> 3) The instruction has been modified since the VM-exit.
>
> 4) The processor is in big real mode and you don't have unrestricted
> guest support in your processor (or you disabled EPT).
What about marking instructions that are not expected to access emulated
memory?
For now, we could WARN_ONCE if they do, which would pave a way to make
unrestricted guest mandatory. Then we would drop instructions that were
not needed with the hope that they won't be.
(This would imply mandatory EPT. Also a benefit, IMO.)
Westmere (the architecture to introduce unrestricted guest) is from
2010, which makes it close to being endangered by expired extended
warranties.
prev parent reply other threads:[~2017-01-20 17:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-12 2:28 [PATCH] KVM: x86: Introduce segmented_write_std Steve Rutherford
2017-01-12 13:40 ` Paolo Bonzini
2017-01-20 16:55 ` Jim Mattson
2017-01-20 17:09 ` Paolo Bonzini
2017-01-20 17:57 ` Radim Krčmář [this message]
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