From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mukesh Rathor Subject: Re: 32bit PAE PV guest on 64bit hypervisor Date: Wed, 22 Apr 2009 18:57:46 -0700 Message-ID: <49EFCB1A.60202@oracle.com> References: Reply-To: mukesh.rathor@oracle.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: xen-devel List-Id: xen-devel@lists.xenproject.org Keir Fraser wrote: > On 14/04/2009 04:39, "Mukesh Rathor" wrote: > .. > Implementing clear_fixmap() with set_pte() is not correct, even on native. > Since it clears high then low, it temporarily leaves you with a possibly > invalid present PTE -- even on native this can cause problems if e.g., the > invalid PTE maps uncacheable I/O memory. > > In our kernel we simply solved this by implementing __set_fixmap() with a > hypercall that could update all 64 bits at once. An alternative is indeed to > clear low then high. Basically, clearing a pte has to be done the opposite > way round to setting a pte. > > -- Keir Just a quick update, I changed to hypercall and it worked. BTW, I also had to increase the __PHYSICAL_MASK_SHIFT in guest (to 40) as I'm on system with 128GB. With both changes in the 32bit PAE guest, it's doing OK now. Thanks for the help. Mukesh