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

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Message-ID: <4E0B0574.4010008@cn.fujitsu.com>
Date:	Wed, 29 Jun 2011 18:59:00 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 05/22] KVM: x86: abstract the operation for read/write
 emulation

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.
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