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Re: [Xen-devel] [PATCH] x86emul: correct LFS et al handling for 64-bit mode
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 12 Dec 2019 14:20:42 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 12 Dec 2019 14:20:50 +0000
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On 12/12/2019 13:05, Jan Beulich wrote:
> On 12.12.2019 12:37, Andrew Cooper wrote:
>> On 12/12/2019 10:11, Jan Beulich wrote:
>>> On 11.12.2019 21:57, Andrew Cooper wrote:
>>>> On 11/12/2019 09:28, Jan Beulich wrote:
>>>>> AMD and friends explicitly specify that 64-bit operands aren't possible
>>>>> for these insns. Nevertheless REX.W isn't fully ignored: It still
>>>>> cancels a possible operand size override (0x66). Intel otoh explicitly
>>>>> provides for 64-bit operands on the respective insn page of the SDM.
>>>>>
>>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>> It is definitely more than just these. Near jumps have per-vendor
>>>> behaviour on how long the instruction is, whereas far jump/calls are in
>>>> the same category as these by the looks of things.
>>> But you don't expect me to fold all of these into one patch, do
>>> you?
>> short jmp certainly not, but far jmp/call is just two extra case
>> statements in this new code block, no?
> Not exactly (the other change would need to be in
> x86_decode_onebyte() and depend on ModRM.reg), but yes, I can
> do this. Yet then it would feel odd to not also deal with the
> near counterparts at the same time. Which in turn would make
> is desirable to also deal with near RET as well. At which
> point we're about to also discuss CALL/JMP with displacement
> operands and Jcc.
>
>>> We have _some_ vendor dependent behavior already, and I'm
>>> slowly adding to it. Our far call/jmp support is rather
>>> incomplete in other ways anyway.
>> There is different truncation behaviour for %rip which needs altering,
>> but that is a separate area of code. Anything else?
> protmode_load_seg() and MOVSXD already have vendor dependent
> code, if that was your question.
I was actually just asking about far jmp/call.
If you're sure that far jmp/call is more complicated than just tweaking
this patch, then fine. Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> For things needing doing see
> above plus LOOP, J[ER]CXZ, SYSENTER, and SYSEXIT as far as I'm
> currently aware.
SYSCALL and SYSRET as well. The way they handle MSR_STAR is vendor
specific, as well as #UD conditions.
I've just noticed that I've still got an XSA-204 followup patch still
outstanding from 2016...
~Andrew
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