RE: [Xen-devel] [PATCH] support protected mode mmio with non-zero CS base

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>      realmode = hvm_realmode(v);
>>      if ( realmode )
>> -        inst_addr = (regs->cs << 4) + regs->eip;
>> +        inst_addr = regs->cs << 4;
>>      else
>> -        inst_addr = regs->eip;
>> +        inst_addr = hvm_get_segment_base(current, seg_cs);
>
>Remove the "if ( realmode ) " and just use the segment base address. The
>base-address in the register should be correct even in realmod, or the
>processor is broken. [I don't think this code is being executed from
>vmxassist - if it is, then that's a different special case!]. 

I intentionally didn't, as at least on VMX the read operation could
be significantly slower than a shift (and due to the indirect call it will
be slower even on SVM).

>Theoretically, you should also check that (eip <= segment.limit), and
>issue GP-fault if not true. 

Again intentionally no: If the original instruction managed to generate
a page fault, than it must have been entirely within limits - otherwise
hardware would have generated a GP fault.

Jan

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