From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Mosberger Date: Fri, 24 Oct 2003 22:21:41 +0000 Subject: RE: [PATCH 2.4.23-pre8] Remove broken prefetching in free_one_pgd() Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org >>>>> On Fri, 24 Oct 2003 15:16:59 -0700, "Luck, Tony" said: Tony> This patch was accepted into 2.5.55, attributed to "davej@uk". Tony> This code will prefetch from beyond the end of the page table Tony> being cleared ... which is clearly a bad thing if the page Tony> table in question is allocated from the last page of memory Tony> (or precedes a hole on a discontig mem system). >> Different arches behave differently, though. In the case of ia64, >> it'a always safe to prefetch (even with lfetch.fault). Tony> Not quite always ... this was how I found the efi trim.bottom Tony> bug, since Linux had allocated a pgd at 0xa00000-16k, and the Tony> lfetch that reached out beyond the end of the page to the Tony> uncacheable address 0xa00000 took an MCA. But don't confuse cause and effect! The MCA was caused by a bad TLB entry. The lfetch only triggered the latent bug (as might have a instruction-prefetch). Tony> A pgd in the last page of a granule that is followed by an uncacheable Tony> address would do the same with lfetch.fault, wouldn't it? No, lfetch to uncacheable translations have no effect. --david