From: "H. Peter Anvin" <hpa@zytor.com>
To: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, bp@alien8.de,
mingo@kernel.org, tglx@linutronix.de
Subject: Re: [PATCH 2/2] make /dev/kmem return error for highmem
Date: Fri, 08 Feb 2013 12:48:20 -0800 [thread overview]
Message-ID: <51156494.3050300@zytor.com> (raw)
In-Reply-To: <20130208202814.E1196596@kernel.stglabs.ibm.com>
On 02/08/2013 12:28 PM, Dave Hansen wrote:
> I was auding the /dev/mem code for more questionable uses of
> __pa(), and ran across this.
>
> My assumption is that if you use /dev/kmem, you expect to be
> able to read the kernel virtual mappings. However, those
> mappings _stop_ as soon as we hit high memory. The
> pfn_valid() check in here is good for memory holes, but since
> highmem pages are still valid, it does no good for those.
>
> Also, since we are now checking that __pa() is being done on
> valid virtual addresses, this might have tripped the new
> check. Even with the new check, this code would have been
> broken with the NUMA remapping code had we not ripped it
> out:
>
It would be great if you could take a stab at fixing /dev/mem and
/dev/kmem... there are a bunch of problems with both which seem to
really translate to "HIGHMEM was never properly implemented"...
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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WARNING: multiple messages have this Message-ID (diff)
From: "H. Peter Anvin" <hpa@zytor.com>
To: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, bp@alien8.de,
mingo@kernel.org, tglx@linutronix.de
Subject: Re: [PATCH 2/2] make /dev/kmem return error for highmem
Date: Fri, 08 Feb 2013 12:48:20 -0800 [thread overview]
Message-ID: <51156494.3050300@zytor.com> (raw)
In-Reply-To: <20130208202814.E1196596@kernel.stglabs.ibm.com>
On 02/08/2013 12:28 PM, Dave Hansen wrote:
> I was auding the /dev/mem code for more questionable uses of
> __pa(), and ran across this.
>
> My assumption is that if you use /dev/kmem, you expect to be
> able to read the kernel virtual mappings. However, those
> mappings _stop_ as soon as we hit high memory. The
> pfn_valid() check in here is good for memory holes, but since
> highmem pages are still valid, it does no good for those.
>
> Also, since we are now checking that __pa() is being done on
> valid virtual addresses, this might have tripped the new
> check. Even with the new check, this code would have been
> broken with the NUMA remapping code had we not ripped it
> out:
>
It would be great if you could take a stab at fixing /dev/mem and
/dev/kmem... there are a bunch of problems with both which seem to
really translate to "HIGHMEM was never properly implemented"...
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
next prev parent reply other threads:[~2013-02-08 20:48 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-08 20:28 [PATCH 1/2] add helper for highmem checks Dave Hansen
2013-02-08 20:28 ` Dave Hansen
2013-02-08 20:28 ` [PATCH 2/2] make /dev/kmem return error for highmem Dave Hansen
2013-02-08 20:28 ` Dave Hansen
2013-02-08 20:48 ` H. Peter Anvin [this message]
2013-02-08 20:48 ` H. Peter Anvin
2013-02-08 20:50 ` [PATCH 1/2] add helper for highmem checks H. Peter Anvin
2013-02-08 20:50 ` H. Peter Anvin
2013-02-08 23:16 ` Dave Hansen
2013-02-08 23:16 ` Dave Hansen
2013-02-09 9:41 ` Borislav Petkov
2013-02-09 9:41 ` Borislav Petkov
2013-02-09 10:47 ` Borislav Petkov
2013-02-09 10:47 ` Borislav Petkov
2013-02-11 17:32 ` Dave Hansen
2013-02-11 17:32 ` Dave Hansen
2013-02-11 18:09 ` H. Peter Anvin
2013-02-11 18:09 ` H. Peter Anvin
2013-02-11 18:28 ` Borislav Petkov
2013-02-11 18:28 ` Borislav Petkov
2013-02-11 19:44 ` H. Peter Anvin
2013-02-11 19:44 ` H. Peter Anvin
2013-02-11 22:34 ` Borislav Petkov
2013-02-11 22:34 ` Borislav Petkov
2013-02-11 22:46 ` H. Peter Anvin
2013-02-11 22:46 ` H. Peter Anvin
2013-02-11 23:00 ` Borislav Petkov
2013-02-11 23:00 ` Borislav Petkov
2013-02-11 23:02 ` H. Peter Anvin
2013-02-11 23:02 ` H. Peter Anvin
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