74 lines
2.5 KiB
Diff
74 lines
2.5 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Mon, 17 Sep 2018 16:29:15 +0200
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Subject: [PATCH] x86/mm/cpa: Optimize same protection check
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When the existing mapping is correct and the new requested page protections
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are the same as the existing ones, then further checks can be omitted and the
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large page can be preserved. The slow path 4k wise check will not come up with
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a different result.
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Before:
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1G pages checked: 2
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1G pages sameprot: 0
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1G pages preserved: 0
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2M pages checked: 540
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2M pages sameprot: 466
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2M pages preserved: 47
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4K pages checked: 800709
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4K pages set-checked: 7668
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After:
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1G pages checked: 2
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1G pages sameprot: 0
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1G pages preserved: 0
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2M pages checked: 538
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2M pages sameprot: 466
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2M pages preserved: 47
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4K pages checked: 560642
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4K pages set-checked: 7668
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Reviewed-by: Dave Hansen <dave.hansen@intel.com>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Bin Yang <bin.yang@intel.com>
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Cc: Mark Gross <mark.gross@intel.com>
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Link: https://lkml.kernel.org/r/20180917143546.424477581@linutronix.de
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Cc: Zhang Ning <ning.a.zhang@intel.com>
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Signed-off-by: Lili Li <lili.li@intel.com>
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---
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arch/x86/mm/pageattr.c | 14 ++++++++++++++
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1 file changed, 14 insertions(+)
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diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
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index 9cc360e539cf..6fc4b05082a6 100644
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--- a/arch/x86/mm/pageattr.c
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+++ b/arch/x86/mm/pageattr.c
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@@ -839,6 +839,20 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
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return 1;
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}
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+ /*
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+ * Optimization: If the requested pgprot is the same as the current
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+ * pgprot, then the large page can be preserved and no updates are
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+ * required independent of alignment and length of the requested
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+ * range. The above already established that the current pgprot is
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+ * correct, which in consequence makes the requested pgprot correct
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+ * as well if it is the same. The static protection scan below will
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+ * not come to a different conclusion.
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+ */
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+ if (pgprot_val(req_prot) == pgprot_val(old_prot)) {
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+ cpa_inc_lp_sameprot(level);
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+ return 0;
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+ }
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+
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/*
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* Make sure that the requested pgprot does not violate the static
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* protections. Check the full large page whether one of the pages
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--
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https://clearlinux.org
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