Re: [PATCH v4] ELF: AT_PAGE_SHIFT_MASK -- supply userspace with available page shifts
From: Kees Cook <hidden>
Date: 2024-02-10 00:41:38
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linux-arch, linux-mm, lkml
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: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. 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. -Kees -- Kees Cook