Re: [PATCH v4] ELF: AT_PAGE_SHIFT_MASK -- supply userspace with available page shifts
From: Alexey Dobriyan <hidden>
Date: 2024-02-13 18:51:05
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linux-arch, linux-mm, lkml
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:quoted
On Mon, Feb 05, 2024 at 04:48:08AM -0800, Kees Cook wrote:quoted
On Mon, Feb 05, 2024 at 12:51:43PM +0300, Alexey Dobriyan wrote:quoted
+#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 !