On 08/17/2012 08:29 PM, Marcelo Tosatti wrote:
> On Thu, Aug 16, 2012 at 05:54:49PM +0300, Avi Kivity wrote:
>> Instead of populating the the entire register file, read in registers
>> as they are accessed, and write back only the modified ones. This
>> saves a VMREAD and VMWRITE on Intel (for rsp, since it is not usually
>> used during emulation), and a two 128-byte copies for the registers.
>>
>
>> @@ -2715,14 +2764,17 @@ int emulator_task_switch(struct x86_emulate_ctxt
>> *ctxt,
>> {
>> int rc;
>>
>> + invalidate_registers(ctxt);
>> ctxt->_eip = ctxt->eip;
>> ctxt->dst.type = OP_NONE;
>>
>> rc = emulator_do_task_switch(ctxt, tss_selector, idt_index, reason,
>> has_error_code, error_code);
>>
>> - if (rc == X86EMUL_CONTINUE)
>> + if (rc == X86EMUL_CONTINUE) {
>> ctxt->eip = ctxt->_eip;
>> + writeback_registers(ctxt);
>> + }
>>
>> return (rc == X86EMUL_UNHANDLEABLE) ? EMULATION_FAILED : EMULATION_OK;
>> }
>
>
> No clear point when emulator register cache is active, when it is
> not (AFAICS this patch does not invalidate registers on emulation start
> (the above being one of the exceptions) does not clear valid bit on
> writeback-to-vcpu-cache on emulation exit).
It is cleared when emulation starts. For the non-insn-emulation entry
points, there is an explicit invalidate. For the emulation entry point,
there is a memset() that clears everything up to _regs, which includes
the cache. This discrepancy isn't nice, but it preexists. I don't know
whether we should decompose the memset() or not, it is rather efficient.
>
> Concern is that emulator can start with cached registers marked as valid
> but in fact are invalid from previous emulation round.
>
> Maybe move invalidate() to init_emulate_ctxt?
>
See the memset() in init_decode_cache().
--
error compiling committee.c: too many arguments to function
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