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

Avi Kivity
2011-06-29T08:37:50Z

On 06/22/2011 05:30 PM, Xiao Guangrong wrote:
> The operations of read emulation and write emulation are very similar, so we
> can abstract the operation of them, in larter patch, it is used to cleanup the
> same code
>
> Signed-off-by: Xiao Guangrong<xiaoguangrong@cn.fujitsu.com>
> ---
> arch/x86/kvm/x86.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 72 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c29ef96..887714f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4056,6 +4056,78 @@ int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
> return 1;
> }
>
> +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.

--
error compiling committee.c: too many arguments to function