>-----Original Message----- >From: Linus Torvalds [mailto:[EMAIL PROTECTED] >Sent: Thursday, January 10, 2008 1:05 PM >To: Pallipadi, Venkatesh >Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; >[EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; >[EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; >[EMAIL PROTECTED]; [EMAIL PROTECTED]; Barnes, Jesse; >[EMAIL PROTECTED]; 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, [EMAIL PROTECTED] wrote: >> >> x86_64: Map only usable memory in identity map. All reserved >memory maps to a >> zero page. > >I don't mind this horribly per se, but why a zero page? > >Accessing that page without mapping it explicitly would be a bug with >your change - if only because you'd get the wrong value! > >So why map it at all? The only thing mapping it can do is to hide bugs. >
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. But, if I not map reserved regions, dd will stop after fist such hole. Even though this may not be a good usage model, I thought there may be apps depending on such things. Having said that, I do not like having dummy zero page there very much. So, if we do not see any regressions due to usages like above, I will be happy to remove mapping reserved regions altogether. Thanks, Venki -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
