From: Michael Ellerman <patch-notifications@ellerman.id.au>
To: Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@ozlabs.org
Cc: aneesh.kumar@linux.vnet.ibm.com
Subject: Re: [1/6] powerpc/mm/radix: Fix off-by-one in split mapping logic
Date: Mon, 22 Oct 2018 20:39:52 +1100 (AEDT) [thread overview]
Message-ID: <42ds1j1lVQz9sDC@ozlabs.org> (raw)
In-Reply-To: <20181019041334.4945-1-mpe@ellerman.id.au>
On Fri, 2018-10-19 at 04:13:29 UTC, Michael Ellerman wrote:
> When we have CONFIG_STRICT_KERNEL_RWX enabled, we try to split the
> kernel linear (1:1) mapping so that the kernel text is in a separate
> page to kernel data, so we can mark the former read-only.
>
> We could achieve that just by always using 64K pages for the linear
> mapping, but we try to be smarter. Instead we use huge pages when
> possible, and only switch to smaller pages when necessary.
>
> However we have an off-by-one bug in that logic, which causes us to
> calculate the wrong boundary between text and data.
>
> For example with the end of the kernel text at 16M we see:
>
> radix-mmu: Mapped 0x0000000000000000-0x0000000001200000 with 64.0 KiB pages
> radix-mmu: Mapped 0x0000000001200000-0x0000000040000000 with 2.00 MiB pages
> radix-mmu: Mapped 0x0000000040000000-0x0000000100000000 with 1.00 GiB pages
>
> ie. we mapped from 0 to 18M with 64K pages, even though the boundary
> between text and data is at 16M.
>
> With the fix we see we're correctly hitting the 16M boundary:
>
> radix-mmu: Mapped 0x0000000000000000-0x0000000001000000 with 64.0 KiB pages
> radix-mmu: Mapped 0x0000000001000000-0x0000000040000000 with 2.00 MiB pages
> radix-mmu: Mapped 0x0000000040000000-0x0000000100000000 with 1.00 GiB pages
>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Series applied to powerpc next.
https://git.kernel.org/powerpc/c/5c6499b7041b43807dfaeda28aa87f
cheers
prev parent reply other threads:[~2018-10-22 10:12 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-19 4:13 [PATCH 1/6] powerpc/mm/radix: Fix off-by-one in split mapping logic Michael Ellerman
2018-10-19 4:13 ` [PATCH 2/6] powerpc/mm/radix: Fix overuse of small pages in splitting logic Michael Ellerman
2018-10-19 4:13 ` [PATCH 3/6] powerpc/mm/radix: Fix small page at boundary when splitting Michael Ellerman
2018-10-19 4:13 ` [PATCH 4/6] powerpc/mm/radix: Remove the retry in the split mapping logic Michael Ellerman
2018-10-19 4:13 ` [PATCH 5/6] powerpc/mm/radix: Simplify " Michael Ellerman
2018-10-19 4:13 ` [PATCH 6/6] powerpc/mm/radix: Display if mappings are exec or not Michael Ellerman
2018-10-22 9:39 ` Michael Ellerman [this message]
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