linux-kernel - Re: [PATCH V2 03/14] x86/set_memory: Add x86_set_memory

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Message-ID: <01d2f33c-6e50-ae88-73ff-84042504c26e@gmail.com>
Date:   Thu, 5 Aug 2021 23:51:43 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
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Subject: Re: [PATCH V2 03/14] x86/set_memory: Add x86_set_memory_enc static
 call support

On 8/5/2021 10:29 PM, Dave Hansen wrote:
> On 8/5/21 7:23 AM, Peter Zijlstra wrote:
>> This is assuming any of this is actually performance critical, based off
>> of this using static_call() to begin with.
> 
> This code is not performance critical.
> 
> I think I sent folks off on a wild goose chase when I asked that we make
> an effort to optimize code that does:
> 
> 	if (some_hyperv_check())
> 		foo();
> 
> 	if (some_amd_feature_check())
> 		bar();
> 
> with checks that will actually compile away when Hyper-V or
> some_amd_feature() is disabled.  That's less about performance and just
> about good hygiene.  I *wanted* to see
> cpu_feature_enabled(X86_FEATURE...) checks.
> 
> Someone suggested using static calls, and off we went...
> 
> Could we please just use cpu_feature_enabled()?
>

Yes, cpu_feature_enabled() works. The target is just to run platform 
code after platform check. I will update this in the next version.