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From: Andrew Morton <akpm@linux-foundation.org>
To: Toshi Kani <toshi.kani@hpe.com>
Cc: mhocko@suse.com, tglx@linutronix.de, mingo@redhat.com,
	hpa@zytor.com, bp@suse.de, catalin.marinas@arm.com,
	guohanjun@huawei.com, will.deacon@arm.com,
	wxf.wang@hisilicon.com, willy@infradead.org,
	cpandya@codeaurora.org, linux-mm@kvack.org, x86@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v2 1/2] mm/vmalloc: Add interfaces to free unmapped page table
Date: Wed, 14 Mar 2018 15:38:35 -0700	[thread overview]
Message-ID: <20180314153835.68e75da3fdc18b27ad0e290c@linux-foundation.org> (raw)
In-Reply-To: <20180314180155.19492-2-toshi.kani@hpe.com>

On Wed, 14 Mar 2018 12:01:54 -0600 Toshi Kani <toshi.kani@hpe.com> wrote:

> On architectures with CONFIG_HAVE_ARCH_HUGE_VMAP set, ioremap()
> may create pud/pmd mappings.  Kernel panic was observed on arm64
> systems with Cortex-A75 in the following steps as described by
> Hanjun Guo.
> 
>  1. ioremap a 4K size, valid page table will build,
>  2. iounmap it, pte0 will set to 0;
>  3. ioremap the same address with 2M size, pgd/pmd is unchanged,
>     then set the a new value for pmd;
>  4. pte0 is leaked;
>  5. CPU may meet exception because the old pmd is still in TLB,
>     which will lead to kernel panic.
> 
> This panic is not reproducible on x86.  INVLPG, called from iounmap,
> purges all levels of entries associated with purged address on x86.
> x86 still has memory leak.
> 
> The patch changes the ioremap path to free unmapped page table(s) since
> doing so in the unmap path has the following issues:
> 
>  - The iounmap() path is shared with vunmap().  Since vmap() only
>    supports pte mappings, making vunmap() to free a pte page is an
>    overhead for regular vmap users as they do not need a pte page
>    freed up.
>  - Checking if all entries in a pte page are cleared in the unmap path
>    is racy, and serializing this check is expensive.
>  - The unmap path calls free_vmap_area_noflush() to do lazy TLB purges.
>    Clearing a pud/pmd entry before the lazy TLB purges needs extra TLB
>    purge.
> 
> Add two interfaces, pud_free_pmd_page() and pmd_free_pte_page(),
> which clear a given pud/pmd entry and free up a page for the lower
> level entries.
> 
> This patch implements their stub functions on x86 and arm64, which
> work as workaround.
> 

whoops.

--- a/include/asm-generic/pgtable.h~mm-vmalloc-add-interfaces-to-free-unmapped-page-table-fix
+++ a/include/asm-generic/pgtable.h
@@ -1014,7 +1014,7 @@ static inline int pud_free_pmd_page(pud_
 {
 	return 0;
 }
-static inline int pmd_free_pte_page(pud_t *pmd)
+static inline int pmd_free_pte_page(pmd_t *pmd)
 {
 	return 0;
 }
_

  reply	other threads:[~2018-03-14 22:38 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-14 18:01 [PATCH v2 0/2] fix memory leak / panic in ioremap huge pages Toshi Kani
2018-03-14 18:01 ` [PATCH v2 1/2] mm/vmalloc: Add interfaces to free unmapped page table Toshi Kani
2018-03-14 22:38   ` Andrew Morton [this message]
2018-03-15 14:27     ` Kani, Toshi
2018-03-14 18:01 ` [PATCH v2 2/2] x86/mm: implement free pmd/pte page interfaces Toshi Kani
2018-03-15  7:39   ` Chintan Pandya
2018-03-15 14:51     ` Kani, Toshi
2018-04-26 14:19   ` Joerg Roedel
2018-04-26 16:21     ` Kani, Toshi
2018-04-26 17:23       ` joro
2018-04-26 17:49         ` Kani, Toshi
2018-04-26 20:07           ` joro
2018-04-26 22:30             ` Kani, Toshi
2018-04-27  7:37               ` joro
2018-04-27 11:39                 ` Michal Hocko
2018-04-27 11:46                   ` joro
2018-04-27 11:52                 ` Chintan Pandya
2018-04-27 12:48                   ` joro
2018-04-27 13:42                     ` Chintan Pandya
2018-04-27 14:31                 ` Kani, Toshi
2018-04-28  9:02                   ` joro
2018-04-28 20:54                     ` Kani, Toshi
2018-04-30  7:30                       ` Chintan Pandya
2018-04-30 13:43                         ` Kani, Toshi

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