linux-kernel - Re: [PATCH AUTOSEL for 4.14 12/67] KVM: x86: add support for emulating UMIP

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Message-ID: <20180319152244.ekaloppjdbtg4gjo@sasha-lappy>
Date:   Mon, 19 Mar 2018 15:22:47 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL for 4.14 12/67] KVM: x86: add support for
 emulating UMIP

On Thu, Mar 08, 2018 at 01:46:39AM -0500, Paolo Bonzini wrote:
>
>
>----- Original Message -----
>> From: "Sasha Levin" <Alexander.Levin@...rosoft.com>
>> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
>> Cc: "Paolo Bonzini" <pbonzini@...hat.com>, "Sasha Levin" <Alexander.Levin@...rosoft.com>
>> Sent: Thursday, March 8, 2018 5:57:36 AM
>> Subject: [PATCH AUTOSEL for 4.14 12/67] KVM: x86: add support for emulating UMIP
>>
>> From: Paolo Bonzini <pbonzini@...hat.com>
>>
>> [ Upstream commit 66336cab3531d3325ebde36a04725dddd0c42cb5 ]
>>
>> The User-Mode Instruction Prevention feature present in recent Intel
>> processor prevents a group of instructions (sgdt, sidt, sldt, smsw, and
>> str) from being executed with CPL > 0. Otherwise, a general protection
>> fault is issued.
>>
>> UMIP instructions in general are also able to trigger vmexits, so we can
>> actually emulate UMIP on older processors.  This commit sets up the
>> infrastructure so that kvm-intel.ko and kvm-amd.ko can set the UMIP
>> feature bit for CPUID even if the feature is not actually available
>> in hardware.
>>
>> Reviewed-by: Wanpeng Li <wanpeng.li@...mail.com>
>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
>
>This is not enough (there were a couple bugs, plus you have not
>added the changes needed to the handle SLDT, STR, etc. in the
>emulator).  But since this is a feature, why is it being backported
>to 4.14, especially without any testing??

Hi Paolo,

They were proposed for stable as part of the automatic patch selection
process. I'll drop this patch.

-- 

Thanks,
Sasha