From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zachary Amsden Subject: [PATCH] Fix lazy mode vmalloc synchronization for paravirt Date: Tue, 21 Aug 2007 18:30:36 -0700 Message-ID: <46CB91BC.2010808@vmware.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------060406000404010004030508" Return-path: Sender: linux-kernel-owner@vger.kernel.org To: Virtualization Mailing List , Linux Kernel Mailing List , Linus Torvalds , Chris Wright Cc: Ben Collins List-Id: virtualization@lists.linuxfoundation.org This is a multi-part message in MIME format. --------------060406000404010004030508 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Found this looping Ubuntu installs with VMI. If unlucky enough to hit a vmalloc sync fault during a lazy mode operation (from an IRQ handler for a module which was not yet populated in current page directory, or from inside copy_one_pte, which touches swap_map, and hit in an unused 4M region), the required PDE update would never get flushed, causing an infinite page fault loop. This bug affects any paravirt-ops backend which uses lazy updates, I believe that makes it a bug in Xen, VMI and lguest. It only happens on LOWMEM kernels. Currently for 2.6.23, but we'll want to backport to -stable as well. Zach --------------060406000404010004030508 Content-Type: text/x-patch; name="i386-linus-vmalloc-paravirt-fix.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="i386-linus-vmalloc-paravirt-fix.patch" Touching vmalloc memory in the middle of a lazy mode update can generate a kernel PDE update, which must be flushed immediately. The fix is to leave lazy mode when doing a vmalloc sync. Signed-off-by: Zachary Amsden diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c index 01ffdd4..fcb38e7 100644 --- a/arch/i386/mm/fault.c +++ b/arch/i386/mm/fault.c @@ -249,9 +249,10 @@ static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address) pmd_k = pmd_offset(pud_k, address); if (!pmd_present(*pmd_k)) return NULL; - if (!pmd_present(*pmd)) + if (!pmd_present(*pmd)) { set_pmd(pmd, *pmd_k); - else + arch_flush_lazy_mmu_mode(); + } else BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k)); return pmd_k; } --------------060406000404010004030508--