From: Kees Cook <keescook@chromium.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Florian Weimer <fweimer@redhat.com>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, x86@kernel.org,
Eric Biederman <ebiederm@xmission.com>,
linux-mm@kvack.org
Subject: Re: [PATCH v4] ELF: AT_PAGE_SHIFT_MASK -- supply userspace with available page shifts
Date: Tue, 13 Feb 2024 11:39:30 -0800 [thread overview]
Message-ID: <202402131138.2CFC8CD5E@keescook> (raw)
In-Reply-To: <54774e70-1e94-44f5-b318-fdfd5115041d@p183>
On Tue, Feb 13, 2024 at 09:51:01PM +0300, Alexey Dobriyan wrote:
> On Fri, Feb 09, 2024 at 04:41:36PM -0800, Kees Cook wrote:
> > On Fri, Feb 09, 2024 at 03:30:37PM +0300, Alexey Dobriyan wrote:
> > > On Mon, Feb 05, 2024 at 04:48:08AM -0800, Kees Cook wrote:
> > > > On Mon, Feb 05, 2024 at 12:51:43PM +0300, Alexey Dobriyan wrote:
> > > > > +#define ARCH_AT_PAGE_SHIFT_MASK \
> > > > > + do { \
> > > > > + u32 val = 1 << 12; \
> > > > > + if (boot_cpu_has(X86_FEATURE_PSE)) { \
> > > > > + val |= 1 << 21; \
> > > > > + } \
> > > > > + if (boot_cpu_has(X86_FEATURE_GBPAGES)) { \
> > > > > + val |= 1 << 30; \
> > > > > + } \
> > > >
> > > > Can we use something besides literal "12", "21", and "30" values here?
> > >
> > > Ehh, no, why? Inside x86_64 the page shifts are very specific numbers,
> > > they won't change.
> >
> > Well, it's nicer to have meaningful words to describe these things.
>
> Not really. Inside specific arch page shifts are fixed, so using names
> is just more macros one need to remember.
>
> If I were to invent names (which I wouldn't), the best names are
>
> PAGE_SHIFT
> PAGE_SHIFT2
> PAGE_SHIFT3
> ...
>
> with PAGE_SHIFT2, PAGE_SHIFT3 being optional macros if arch doesn't support
> multiple page sizes.
>
> > In fact, PAGE_SHIFT already exists for 12, and HPAGE_SHIFT already exists
> > for 21. Please use those, and add another, perhaps GBPAGE_SHIFT, for 30.
>
> HPAGE_SHIFT is bad name, H doesn't describe anything unless arch is
> known. Hugepages is marketing name. If GBPAGE_SHIFT is good name,
> then HPAGE_SHIFT is bad name, it should've been MBPAGE_SHIFT, which
> wrong because it is 2 MiB not 1 MiB.
>
> BTW parisc has REAL_HPAGE_SHIFT !
Sure, I mean, we've got an x86-specific function here, so let's use the
x86-specific macros we already have for 12 and 21, and then add the
missing one for 30.
--
Kees Cook
prev parent reply other threads:[~2024-02-13 19:39 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-05 9:51 [PATCH v4] ELF: AT_PAGE_SHIFT_MASK -- supply userspace with available page shifts Alexey Dobriyan
2024-02-05 12:48 ` Kees Cook
2024-02-09 12:30 ` Alexey Dobriyan
2024-02-10 0:41 ` Kees Cook
2024-02-13 18:51 ` Alexey Dobriyan
2024-02-13 19:39 ` Kees Cook [this message]
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