On Thu, Nov 20, 2008 at 10:48:21AM +0100, Marcelo Tosatti wrote: > Hi Aurelien, Hi,
> On Wed, Nov 12, 2008 at 08:00:37PM +0100, Aurelien Jarno wrote: > > Hi, > > > > Starting with kvm-76 (and including kvm-79), Hurd does not boot anymore > > under KVM. The ext2fs translator issues a strange error message: > > > > | Hurd server bootstrap: ext2fs.static[device:hd0s3] execext2fs.static: > > /build/bui > > | ldd/hurd-20080607/build-tree/hurd/ext2fs/dir.c:494: dirscanblock: > > Assertion `dp- > > | >dn->dirents[idx] == -1 || dp->dn->dirents[idx] == nentries' failed. > > - > > | >dn->dirents[idx] == -1 || dp->dn->dirents[idx] == nentries' failed. > > > > Bisecting the problem, I have found that it comes from this patch: > > > > | 641fb03992b20aa640781a245f6b7136f0b845e4 is first bad commit > > | commit 641fb03992b20aa640781a245f6b7136f0b845e4 > > | Author: Marcelo Tosatti <[EMAIL PROTECTED]> > > | Date: Tue Sep 23 13:18:39 2008 -0300 > > | > > | KVM: MMU: out of sync shadow core v2 > > | > > | Allow guest pagetables to go out of sync. > > | > > | Signed-off-by: Marcelo Tosatti <[EMAIL PROTECTED]> > > | Signed-off-by: Avi Kivity <[EMAIL PROTECTED]> > > > > The problem can be workarounded loading the kvm module with > > oos_shadow=0. > > > > The easiest way to reproduce the problem is to download a ready to use > > Hurd image [1]. The error message from the ext2fs translator is not > > exactly the same, but it still fails. > > It seems Hurd does not always explicitly flush the TLB via cr0/cr3/cr4 > writes or invlpg after updating pagetables. Debugging shows that OOS is > properly syncing the sptes wrt the guest pagetables, and that all pages > are synced before guest re-entry on TLB flush exits. Thanks for your investigation. > The Intel TLB doc says (5.1 "Invalidation Instructions"): > > (Other instructions and operations may invalidate entries in the TLBs > and the paging structure caches, but the instructions identified above > are recommended.) > > As a test, syncing on every exit makes it happy: > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 7a2aeba..47e2550 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -3052,6 +3052,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, > struct kvm_run *kvm_run) > > kvm_lapic_sync_from_vapic(vcpu); > > + kvm_mmu_sync_roots(vcpu); > + > r = kvm_x86_ops->handle_exit(kvm_run, vcpu); > out: > return r; > > It would be necessary to confirm this by hacking Hurd to flush on every > pagetable update. Perhaps something like > > RCS file: /sources/hurd/gnumach/i386/intel/pmap.c,v > retrieving revision 1.4.2.22 > diff -u -r1.4.2.22 pmap.c > --- pmap.c 11 Nov 2008 02:24:18 -0000 1.4.2.22 > +++ pmap.c 20 Nov 2008 12:47:01 -0000 > @@ -82,7 +82,7 @@ > #include <i386/proc_reg.h> > #include <i386/locore.h> > > -#define WRITE_PTE(pte_p, pte_entry) *(pte_p) = (pte_entry); > +#define WRITE_PTE(pte_p, pte_entry) *(pte_p) = (pte_entry); > flush_tlb(); > > /* > * Private data structures. > > I have tried this patch, but it doesn't change anything. I'll try to see if there are more place when the PTE is written. -- .''`. Aurelien Jarno | GPG: 1024D/F1BCDB73 : :' : Debian developer | Electrical Engineer `. `' [EMAIL PROTECTED] | [EMAIL PROTECTED] `- people.debian.org/~aurel32 | www.aurel32.net -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
