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Subject[tip:x86/mm] x86/mm/cpa: Avoid static protection checks on unmap
Commit-ID:  69c31e69df3d2efc4ad7f53d500fdd920d3865a4
Gitweb: https://git.kernel.org/tip/69c31e69df3d2efc4ad7f53d500fdd920d3865a4
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Mon, 17 Sep 2018 16:29:13 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 27 Sep 2018 20:39:38 +0200

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

---
arch/x86/mm/pageattr.c | 7 +++++++
1 file changed, 7 insertions(+)

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;

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