Re: [Xen-devel] [PATCH v2 2/2] x86/vm_event: Allow overwriting Xen's i-cache used for emulation

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

On Sat, Sep 17, 2016 at 10:40 AM, Razvan Cojocaru
<rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 09/15/16 19:51, Tamas K Lengyel wrote:
>> When emulating instructions Xen's emulator maintains a small i-cache fetched
>> from the guest memory. This patch extends the vm_event interface to allow
>> overwriting this i-cache via a buffer returned in the vm_event response.
>>
>> When responding to a SOFTWARE_BREAKPOINT event (INT3) the monitor subscriber
>> normally has to remove the INT3 from memory - singlestep - place back INT3
>> to allow the guest to continue execution. This routine however is susceptible
>> to a race-condition on multi-vCPU guests. By allowing the subscriber to 
>> return
>> the i-cache to be used for emulation it can side-step the problem by 
>> returning
>> a clean buffer without the INT3 present.
>>
>> As part of this patch we rename hvm_mem_access_emulate_one to
>> hvm_emulate_one_vm_event to better reflect that it is used in various 
>> vm_event
>> scenarios now, not just in response to mem_access events.
>>
>> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
>> ---
>> Cc: Paul Durrant <paul.durrant@xxxxxxxxxx>
>> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>
>> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
>> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
>> Cc: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
>> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>> Cc: Julien Grall <julien.grall@xxxxxxx>
>>
>> v2: rework hvm_mem_access_emulate_one switch statement
>>     add BUILD_BUG_ON to ensure internal and vm_event buffer sizes match
>>
>> Note: this patch has now been fully tested and works as intended
>
> Acked-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
>
> On a side note, I see that you're using an email address that's
> different from the one in MAINTAINERS. Should we update the MAINTAINERS
> file?

It's fine for now (both go to the same place at the end anyway).

Tamas

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