Avi Kivity wrote:
> Laurent Vivier wrote:
>> vmx.c uses x86_decode_prefix() instead of get_io_count().
>>
>> static int handle_io(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>> {
>> u64 exit_qualification;
>> @@ -1831,8 +1780,32 @@
>> port = exit_qualification >> 16;
>> address = 0;
>> if (string) {
>> - if (rep && !get_io_count(vcpu, &count))
>> + int mode;
>> + u64 inst;
>> + gva_t rip;
>> + struct x86_prefix prefix;
>> + u32 cs_ar = vmcs_read32(GUEST_CS_AR_BYTES);
>> + unsigned long addr_mask;
>> +
>> + mode = (vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_VM) ?
>> + X86EMUL_MODE_REAL : (cs_ar & AR_L_MASK)
>> + ? X86EMUL_MODE_PROT64 : (cs_ar & AR_DB_MASK)
>> + ? X86EMUL_MODE_PROT32 : X86EMUL_MODE_PROT16;
>> +
>> + rip = vmcs_readl(GUEST_RIP);
>> + if (mode != X86EMUL_MODE_PROT64)
>> + rip += vmcs_readl(GUEST_CS_BASE);
>> + if (emulator_read_std(rip, &inst, sizeof(inst), vcpu)
>> + != X86EMUL_CONTINUE)
>> + return 1;
>> +
>> + if (x86_decode_prefix(mode, (u8*)&inst, &prefix) == -1)
>> return 1;
>> +
>> + addr_mask = (~0ULL >> (64 - (prefix.ad_bytes <<3)));
>> + if (rep)
>> + count = vcpu->regs[VCPU_REGS_RCX] & addr_mask;
>> +
>> address = vmcs_readl(GUEST_LINEAR_ADDRESS);
>> }
>> return kvm_setup_pio(vcpu, kvm_run, in, size, count, string, down,
>
> How about just calliing emulate_instruction() from here (just for the
> string case)? That will eliminate all the setup code.
But this setup is in emulate_instruction() so it will be executed anyway.
> x86_emulate_memop() will need to be extended to decode ins/outs, but
> that's fairly easy.
X86_decode_prefix() is a subset of instruction decoding part of
x86_emulate_memop(), kvm_setup_pio() can be seen as a subset of instruction
emulating part of x86_emulate_memop(). So I think in term of performance it is
better to do like that, but I agree by doing:
if (string)
return emulate_instruction(vcpu, kvm_run, 0, 0);
else
return kvm_setup_pio(vcpu, kvm_run, in, size, port);
it is more more ... more simple.
If you prefer simplicity, I can do like that ?
(but I know you prefer simplicity...)
BTW, I think PATCH 1,2 and 3 should be applied anyway because they allow to
introduce the separation between instruction decoding and instruction emulation
requested by the TODO "Split the emulator into two functions: one to decode into
the emulation context, and the other to actually execute the instruction."
Laurent
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