Re: [PATCH] x86/cpu: Add INVLPGB CPU feature flag to /proc/cpuinfo

[Dave Hansen]

On 3/18/26 11:23, Yongting Lin wrote:
> On Wed, 18 Mar 2026 10:58:26 -0700, Dave Hansen wrote:
>> On 3/18/26 10:52, Yongting Lin wrote:
>>> commit 767ae437a32d ("x86/mm: Add INVLPGB feature and Kconfig entry")
>>> introduced support for the INVLPGB instruction as a fast TLB
>>> invalidation mechanism. However, no corresponding CPU feature flag is
>>> exposed via /proc/cpuinfo.
>>
>> The patch is probably OK, but the changelog is insufficient. Could you
>> please read through:
>>
>>        Documentation/arch/x86/cpuinfo.rst
>>
>> and use that structure to construct a justification for why this feature
>> is needed?
> 
> Hi Dave, the invlpgb is a new ISA for newly AMD processors to issue a BROADCAST
> operation to invalidate TLB entry in all remote CPUS, avoiding a cost of
> IPI tlb flush operations.

Heh, thanks for the background.

> It should be visible to Linux user to be aware of this new feature as well
> as application programs.

I get it. But this doesn't tell me *why*.

Did you happen to read the documentation I referenced above and asked
you to read? I was hoping after you read it, you would understand which
kinds of features we want in /proc/cpuinfo and which ones we don't.
Then, you would be prepared to make a strong case for *why*.