Re: [PATCH v2 05/22] KVM: x86: abstract the operation for read/write emulation

Xiao Guangrong
2011-06-29T10:59:00Z

On 06/29/2011 04:37 PM, Avi Kivity wrote:

>> +struct read_write_emulator_ops {
>> + int (*read_write_prepare)(struct kvm_vcpu *vcpu, void *val,
>> + int bytes);
>> + int (*read_write_emulate)(struct kvm_vcpu *vcpu, gpa_t gpa,
>> + void *val, int bytes);
>> + int (*read_write_mmio)(struct kvm_vcpu *vcpu, gpa_t gpa,
>> + int bytes, void *val);
>> + int (*read_write_exit_mmio)(struct kvm_vcpu *vcpu, gpa_t gpa,
>> + void *val, int bytes);
>> + bool write;
>> +};
>
>
> Interesting!
>
> This structure combines two unrelated operations, though. One is the internals of the iteration on a virtual address that is split to various physical addresses. The other is the interaction with userspace on mmio exits. They should be split, but I think it's fine to do it in a later patch. This series is long enough already.
>
> I was also annoyed by the duplication. They way I thought of fixing it is having gva_to_gpa() return two gpas, and having the access function accept gpa vectors. The reason was so that we can implemented locked cross-page operations (which we now emulate as unlocked writes).
>
> But I think we can do without it, and instead emulated locked cross-page ops by stalling all other vcpus while we write, or by unmapping the pages involved. It isn't pretty but it doesn't need to be fast since it's a very rare operation. So I think we can go with your approach.
>

OK, i'll post it in the separate patchset, thanks, Avi.