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

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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@xxxxxxxxxxxxxx>
---
  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

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