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Date: Tue, 15 Mar 2022 09:57:30 -0700 From: Ira Weiny <ira.weiny@...el.com> To: Dave Hansen <dave.hansen@...el.com> Cc: Dave Hansen <dave.hansen@...ux.intel.com>, "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>, "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 5/5] x86/pkeys: Standardize on u8 for pkey type On Tue, Mar 15, 2022 at 09:03:26AM -0700, Dave Hansen wrote: > On 3/15/22 08:53, Ira Weiny wrote: > > On Mon, Mar 14, 2022 at 04:49:12PM -0700, Dave Hansen wrote: > >> On 3/10/22 16:57, ira.weiny@...el.com wrote: > >>> From: Ira Weiny <ira.weiny@...el.com> > >>> > >>> The number of pkeys supported on x86 and powerpc are much smaller than a > >>> u16 value can hold. It is desirable to standardize on the type for > >>> pkeys. powerpc currently supports the most pkeys at 32. u8 is plenty > >>> large for that. > >>> > >>> Standardize on the pkey types by changing u16 to u8. > >> > >> How widely was this intended to "standardize" things? Looks like it may > >> have missed a few spots. > > > > Sorry I think the commit message is misleading you. The justification of u8 as > > the proper type is that no arch has a need for more than 255 pkeys. > > > > This specific patch was intended to only change x86. Per that goal I don't see > > any other places in x86 which uses u16 after this patch. > > > > $ git grep u16 arch/x86 | grep key > > arch/x86/events/intel/uncore_discovery.c: const u16 *type_id = key; > > arch/x86/include/asm/intel_pconfig.h: u16 keyid; > > arch/x86/include/asm/mmu.h: u16 pkey_allocation_map; > > arch/x86/include/asm/pkeys.h: u16 all_pkeys_mask = ((1U << arch_max_pkey()) - 1); > > I was also looking at the generic mm code. Ah yea that needs to be sorted out too I think. > > >> Also if we're worried about the type needing to changY or with the wrong > >> type being used, I guess we could just to a pkey_t typedef. > > > > I'm not 'worried' about it. But I do think it makes the code cleaner and more > > self documenting. > > Yeah, consistency is good. Do you mind taking a look at how a pkey_t > would look, and also seeing how much core mm code should use it? I don't mind at all. Ira
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