From: Thomas Gleixner <tglx@linutronix.de> Date: Mon, 17 Sep 2018 14:29:13 +0000 (+0200) Subject: x86/mm/cpa: Avoid static protection checks on unmap X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=69c31e69df3d2efc4ad7f53d500fdd920d3865a4;p=openwrt%2Fstaging%2Fblogic.git x86/mm/cpa: Avoid static protection checks on unmap If the new pgprot has the PRESENT bit cleared, then conflicts vs. RW/NX are completely irrelevant. Before: 1G pages checked: 2 1G pages sameprot: 0 1G pages preserved: 0 2M pages checked: 540 2M pages sameprot: 466 2M pages preserved: 47 4K pages checked: 800770 4K pages set-checked: 7668 After: 1G pages checked: 2 1G pages sameprot: 0 1G pages preserved: 0 2M pages checked: 540 2M pages sameprot: 466 2M pages preserved: 47 4K pages checked: 800709 4K pages set-checked: 7668 Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Dave Hansen <dave.hansen@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Bin Yang <bin.yang@intel.com> Cc: Mark Gross <mark.gross@intel.com> Link: https://lkml.kernel.org/r/20180917143546.245849757@linutronix.de --- diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index cdf52eb86f3a..8f9083eb21ac 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -526,6 +526,13 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long start, pgprotval_t forbidden, res; unsigned long end; + /* + * There is no point in checking RW/NX conflicts when the requested + * mapping is setting the page !PRESENT. + */ + if (!(pgprot_val(prot) & _PAGE_PRESENT)) + return prot; + /* Operate on the virtual address */ end = start + npg * PAGE_SIZE - 1;