From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Luck, Tony" Date: Fri, 24 Oct 2003 22:16:59 +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 > 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). Not quite always ... this was how I found the efi trim.bottom bug, since Linux had allocated a pgd at 0xa00000-16k, and the lfetch that reached out beyond the end of the page to the uncacheable address 0xa00000 took an MCA. A pgd in the last page of a granule that is followed by an uncacheable address would do the same with lfetch.fault, wouldn't it? -Tony