From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: sysenter/syscall support for 32-on-64 guests? Date: Thu, 28 Feb 2008 17:14:21 +0000 Message-ID: <47C6F9FD.76E4.0078.0@novell.com> References: <47C6E634.3080609@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <47C6E634.3080609@goop.org> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jeremy Fitzhardinge Cc: Keir Fraser , Xen-devel , Ian Campbell List-Id: xen-devel@lists.xenproject.org >>> Jeremy Fitzhardinge 28.02.08 17:49 >>> >I just spent quite a while working out why pvops-Xen kernels weren't=20 >booting for me in a 64-bit hypervisor. It turned out to be because=20 >32-on-64 supports SEP even though 32-on-32 doesn't, so the guest = kernel=20 >was trying to use it without having set up the Xen side, resulting in=20 >syscalls jumping to 0:0, generating a mysterious GP. Once I worked = that=20 >out, the fix was simple, of course. > >Anyway, I wonder if you had a specific reason for allowing this, other=20 >than "because we can"? It seems to me that we should try to minimize=20 >the number of differences between 32-on-32 and 32-on-64 as much as = possible. Since int80 cannot be directly passed to the guest (as in 32-on-32), it seemed reasonable to cut on the overhead of syscalls by at least allowing this (and syscall could also be made work now that the vdso stuff is unified in 2.6.25) - for obvious reasons it still goes through = the hypervisor, but gets there faster Jan