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Re: [PATCH 1/2] x86/pv: Rework guest_io_okay() to return X86EMUL_*
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 1 Oct 2024 11:02:21 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 01 Oct 2024 10:02:27 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 01/10/2024 8:11 am, Jan Beulich wrote:
> On 30.09.2024 18:18, Andrew Cooper wrote:
>> @@ -190,10 +192,12 @@ static bool guest_io_okay(unsigned int port, unsigned
>> int bytes,
>> toggle_guest_pt(v);
>>
>> if ( (x.mask & (((1 << bytes) - 1) << (port & 7))) == 0 )
>> - return true;
>> + return X86EMUL_OKAY;
>> }
>>
>> - return false;
>> + x86_emul_hw_exception(X86_EXC_GP, 0, ctxt);
> do_general_protection() has
>
> /* Pass on GPF as is. */
> pv_inject_hw_exception(X86_EXC_GP, regs->error_code);
>
> which may make a difference in case the insn changes under our feet.
It would make a difference if we chose to raise #GP[non-0].
But, see how the call to pv_emulate_privileged_op() is guarded on
error_code == 0.
Prior X86EMUL_UNHANDLEABLE can't ever have raised anything other than
#GP[0], (excusing cases of memory corruption in regs->error_code).
So, there is not a change in behaviour, even if the reason why is
less-than-obvious.
~Andrew
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