Messages in this thread | | | Subject | RE: [patch 02/11] PAT x86: Map only usable memory in x86_64 identity map and kernel text | Date | Thu, 10 Jan 2008 14:27:10 -0800 | From | "Pallipadi, Venkatesh" <> |
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>-----Original Message----- >From: Linus Torvalds [mailto:torvalds@linux-foundation.org] >Sent: Thursday, January 10, 2008 2:15 PM >To: Pallipadi, Venkatesh >Cc: ak@muc.de; ebiederm@xmission.com; rdreier@cisco.com; >gregkh@suse.de; airlied@skynet.ie; davej@redhat.com; >mingo@elte.hu; tglx@linutronix.de; akpm@linux-foundation.org; >arjan@infradead.org; Barnes, Jesse; davem@davemloft.net; >linux-kernel@vger.kernel.org; Siddha, Suresh B >Subject: RE: [patch 02/11] PAT x86: Map only usable memory in >x86_64 identity map and kernel text > > > >On Thu, 10 Jan 2008, Pallipadi, Venkatesh wrote: >> >> Yes. I had those pages not mapped at all earlier. The reason >I switched >> to zero page is to continue support cases like: >> BIOS-e820: 0000000000000000 - 000000000009cc00 (usable) >> BIOS-e820: 000000000009cc00 - 00000000000a0000 (reserved) >> BIOS-e820: 00000000000cc000 - 00000000000d0000 (reserved) >> BIOS-e820: 00000000000e4000 - 0000000000100000 (reserved) >> BIOS-e820: 0000000000100000 - 00000000cff60000 (usable) >> >> In this case if some one does a dd of /dev/mem before they >can read the >> contents of usable memory in 0x100000-0xcff60000 range. > >Well, I think that /dev/mem should simply give them the right >info. That's >what people use /dev/mem for - doing things like reading BIOS >images etc. > >So returning *either* a zero page *or* stopping at the first >hole is both >equally wrong. >
I was not fully clear in my earlier email. Mapping /dev/mem would still work with our changes. As they go through proper map interface. It is the dd of dev mem which does the read that has the problem. I was wondering of apps using dd.
Thanks, Venki
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