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  1. 17 1月, 2020 15 次提交
  3. 15 1月, 2020 20 次提交
  5. 02 1月, 2020 1 次提交
  7. 27 12月, 2019 4 次提交
    • T
      x86/mm/cpa: Prevent large page split when ftrace flips RW on kernel text · da57ae3d
      由 Thomas Gleixner 提交于 
      commit 7af0145067bc429a09ac4047b167c0971c9f0dc7 upstream.

ftrace does not use text_poke() for enabling trace functionality. It uses
its own mechanism and flips the whole kernel text to RW and back to RO.

The CPA rework removed a loop based check of 4k pages which tried to
preserve a large page by checking each 4k page whether the change would
actually cover all pages in the large page.

This resulted in endless loops for nothing as in testing it turned out that
it actually never preserved anything. Of course testing missed to include
ftrace, which is the one and only case which benefitted from the 4k loop.

As a consequence enabling function tracing or ftrace based kprobes results
in a full 4k split of the kernel text, which affects iTLB performance.

The kernel RO protection is the only valid case where this can actually
preserve large pages.

All other static protections (RO data, data NX, PCI, BIOS) are truly
static.  So a conflict with those protections which results in a split
should only ever happen when a change of memory next to a protected region
is attempted. But these conflicts are rightfully splitting the large page
to preserve the protected regions. In fact a change to the protected
regions itself is a bug and is warned about.

Add an exception for the static protection check for kernel text RO when
the to be changed region spawns a full large page which allows to preserve
the large mappings. This also prevents the syslog to be spammed about CPA
violations when ftrace is used.

The exception needs to be removed once ftrace switched over to text_poke()
which avoids the whole issue.

Fixes: 585948f4f695 ("x86/mm/cpa: Avoid the 4k pages check completely")
Reported-by: NSong Liu <songliubraving@fb.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Tested-by: NSong Liu <songliubraving@fb.com>
Reviewed-by: NSong Liu <songliubraving@fb.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908282355340.1938@nanos.tec.linutronix.deSigned-off-by: NShile Zhang <shile.zhang@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
      da57ae3d
    • Q
      x86/mm: Remove unused variable 'old_pte' · 9737e3ab
      由 Qian Cai 提交于 
      commit 24c41220659ecc5576c34c6f23537f8d3949fb05 upstream.

The commit 3a19109e ("x86/mm: Fix try_preserve_large_page() to
handle large PAT bit") fixed try_preserve_large_page() by using the
corresponding pud/pmd prot/pfn interfaces, but left a variable unused
because it no longer used pte_pfn().

Later, the commit 8679de0959e6 ("x86/mm/cpa: Split, rename and clean up
try_preserve_large_page()") renamed try_preserve_large_page() to
__should_split_large_page(), but the unused variable remains.

arch/x86/mm/pageattr.c: In function '__should_split_large_page':
arch/x86/mm/pageattr.c:741:17: warning: variable 'old_pte' set but not
used [-Wunused-but-set-variable]

Fixes: 3a19109e ("x86/mm: Fix try_preserve_large_page() to handle large PAT bit")
Signed-off-by: NQian Cai <cai@lca.pw>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: dave.hansen@linux.intel.com
Cc: luto@kernel.org
Cc: peterz@infradead.org
Cc: toshi.kani@hpe.com
Cc: bp@alien8.de
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/20190301152924.94762-1-cai@lca.pwSigned-off-by: NShile Zhang <shile.zhang@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
      9737e3ab
    • T
      x86/mm/cpa: Avoid the 4k pages check completely · d5c07e58
      由 Thomas Gleixner 提交于 
      commit 585948f4f695b07204702cfee0f828424af32aa7 upstream.

The extra loop which tries hard to preserve large pages in case of conflicts
with static protection regions turns out to be not preserving anything, at
least not in the experiments which have been conducted.

There might be corner cases in which the code would be able to preserve a
large page oaccsionally, but it's really not worth the extra code and the
cycles wasted in the common case.

Before:

 1G pages checked:                    2
 1G pages sameprot:                   0
 1G pages preserved:                  0
 2M pages checked:                  541
 2M pages sameprot:                 466
 2M pages preserved:                 47
 4K pages checked:                  514
 4K pages set-checked:             7668

After:
 1G pages checked:                    2
 1G pages sameprot:                   0
 1G pages preserved:                  0
 2M pages checked:                  538
 2M pages sameprot:                 466
 2M pages preserved:                 47
 4K pages set-checked:             7668
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NDave 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/20180917143546.589642503@linutronix.deSigned-off-by: NShile Zhang <shile.zhang@linux.alibaba.com>
Acked-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
      d5c07e58
    • T
      x86/mm/cpa: Do the range check early · d935f3fe
      由 Thomas Gleixner 提交于 
      commit 9cc9f17a5a0a8564b41b7c5c460e7f078c42d712 upstream.

To avoid excessive 4k wise checks in the common case do a quick check first
whether the requested new page protections conflict with a static
protection area in the large page. If there is no conflict then the
decision whether to preserve or to split the page can be made immediately.

If the requested range covers the full large page, preserve it. Otherwise
split it up. No point in doing a slow crawl in 4k steps.

Before:

 1G pages checked:                    2
 1G pages sameprot:                   0
 1G pages preserved:                  0
 2M pages checked:                  538
 2M pages sameprot:                 466
 2M pages preserved:                 47
 4K pages checked:               560642
 4K pages set-checked:             7668

After:

 1G pages checked:                    2
 1G pages sameprot:                   0
 1G pages preserved:                  0
 2M pages checked:                  541
 2M pages sameprot:                 466
 2M pages preserved:                 47
 4K pages checked:                  514
 4K pages set-checked:             7668
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NDave 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/20180917143546.507259989@linutronix.deSigned-off-by: NShile Zhang <shile.zhang@linux.alibaba.com>
Acked-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
      d935f3fe