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Date: Thu, 7 Mar 2024 15:32:53 -0800
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Subject: Re: [RFC PATCH 1/3] x86/mm: fix LAM cr3 mask inconsistency during
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To: Yosry Ahmed <yosryahmed@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
 Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Borislav Petkov <bp@alien8.de>, Peter Zijlstra <peterz@infradead.org>,
 Andy Lutomirski <luto@kernel.org>,
 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, x86@kernel.org,
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From: Dave Hansen <dave.hansen@intel.com>
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On 3/7/24 15:21, Yosry Ahmed wrote:
>>> The "set_" naming bugs me in both of the sites that get modified here.
>>> I'd be with a new name that fits better, if we can think of one.
>> Is it because it's not clear we are updating cpu_tlbstate (in which case
>> I think update_cpu_tlbstate_lam() is an improvement), or is it because
>> the function returns a value now? 

That's part of it.

>> If the latter we can put "return" in the name somewhere, or keep
>> the function void and pass in an output parameter.
No, adding a "_return" won't make it better.

> Or we can avoid returning a value from the helper and avoid passing an
> mm. The callers would be more verbose, they'll have to call
> mm_lam_cr3_mask() and mm_untag_mask() and pass the results into the
> helper (set_tlbstate_lam_mode() or update_cpu_tlbstate_lam()). Another
> advantage of this is that we can move the READ_ONCE to
> switch_mm_irqs_off() and keep the comment here.


One thing I don't like about set_tlbstate_lam_mode() is that it's not
obvious that it's writing to "cpu_tlbstate" and its right smack in the
middle of a bunch of other writers to the same thing.

But I'm also not sure that open-coding it at its three call sites makes
things better overall.

I honestly don't have any brilliant suggestions.