linux-kernel - Re: [PATCH] x86: svm: make wbinvd faster

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Message-ID: <54F4969B.8080806@amd.com>
Date:	Mon, 2 Mar 2015 10:58:03 -0600
From:	Joel Schopp <joel.schopp@....com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	Bandan Das <bsd@...hat.com>
CC:	Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	David Kaplan <David.Kaplan@....com>,
	Joerg Roedel <joro@...tes.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	<linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86: svm: make wbinvd faster


On 03/02/2015 10:03 AM, Radim Krčmář wrote:
> 2015-03-02 10:25-0500, Bandan Das:
>> Radim Krčmář <rkrcmar@...hat.com> writes:
>>> 2015-03-01 21:29-0500, Bandan Das:
>>>> Joel Schopp <joel.schopp@....com> writes:
>>>>> +static int wbinvd_interception(struct vcpu_svm *svm)
>>>>> +{
>>>>> +	kvm_emulate_wbinvd(&svm->vcpu);
>>>>> +	skip_emulated_instruction(&svm->vcpu);
>>>>> +	return 1;
>>>>> +}
>>>> Can't we merge this to kvm_emulate_wbinvd, and just call that function
>>>> directly for both vmx and svm ?
>>> kvm_emulate_wbinvd() lives in x86.c and skip_emulated_instruction() is
>>> from svm.c/vmx.c:  so we'd have to create a new x86 op and change the
>>> emulator code as well ... it's probably better like this.
>> There's already one - kvm_x86_ops->skip_emulated_instruction
> My bad, its usage is inconsistent and I only looked at two close
> interceptions where it was used ... kvm_emulate_cpuid() calls
> kvm_x86_ops->skip_emulated_instruction(), while kvm_emulate_halt() and
> kvm_emulate_hypercall() need an external skip.
>
> We do "skip" the instruction with kvm_emulate(), so automatically
> skipping the instruction on kvm_emulate_*() makes sense:
>   1. rename kvm_emulate_halt() and kvm_emulate_wbinvd() to accommodate
>      callers that don't want to skip
>   2. introduce kvm_emulate_{halt,wbinvd}() and move the skip to to
>      kvm_emulate_{halt,wbinvd,hypercall}()
>
> The alternative is to remove kvm_x86_ops->skip_emulated_instruction():
>   1. remove skip from kvm_emulate_cpuid() and modify callers
>   2. move kvm_complete_insn_gp to a header file and use
>      skip_emulated_instruction directly
>   3. remove unused kvm_x86_ops->skip_emulated_instruction()
>
> Which one do you prefer?
I prefer renaming them,  ie kvm_emulate_wbinvd_noskip(), and making the 
existing ones, ie kvm_emulate_wbinvd() call the noskip verion and add a 
skip similar to how wbinvd_interception above does.  I can send out a 
patch later today with that rework.
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