Dang! The mail relay at OVH has blacklisted Paul's address :-\
<paulus@xxxxxxxxx>: host smtp.samba.org[144.76.82.148] said: 550-blacklisted at
zen.spamhaus.org 550 https://www.spamhaus.org/sbl/query/SBL370982 (in reply
to RCPT TO command)
Cc'ing Paul at ozlabs.org
On Fri, 15 Sep 2017 10:48:39 +1000
David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Thu, Sep 14, 2017 at 11:56:25PM +0200, Greg Kurz wrote:
> > The following program causes a kernel oops:
> >
> > #include <sys/types.h>
> > #include <sys/stat.h>
> > #include <fcntl.h>
> > #include <sys/ioctl.h>
> > #include <linux/kvm.h>
> >
> > main()
> > {
> > int fd = open("/dev/kvm", O_RDWR);
> > ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_PPC_HTM);
> > }
> >
> > This happens because when using the global KVM fd with
> > KVM_CHECK_EXTENSION, kvm_vm_ioctl_check_extension() gets
> > called with a NULL kvm argument, which gets dereferenced
> > in is_kvmppc_hv_enabled(). Spotted while reading the code.
> >
> > Let's use the hv_enabled fallback variable, like everywhere
> > else in this function.
> >
> > Fixes: 23528bb21ee2 ("KVM: PPC: Introduce KVM_CAP_PPC_HTM")
> > Cc: stable@xxxxxxxxxxxxxxx # v4.7+
> > Signed-off-by: Greg Kurz <groug@xxxxxxxx>
>
> I don't think this is right. I'm pretty sure you want to fall back to
> hv_enabled *only when* kvm is NULL. Otherwise if you have a PR guest
> on an HV capable machine, this will give the wrong answer, when called
> for that specific VM.
>
Hmmm... this is what we get with this patch applied:
open("/dev/kvm", O_RDWR) = 3
ioctl(3, KVM_CHECK_EXTENSION, 0x84) = 1 <== if HV is present
ioctl(3, KVM_CREATE_VM, 0x1) = 4 <== HV
ioctl(4, KVM_CHECK_EXTENSION, 0x84) = 1
ioctl(3, KVM_CREATE_VM, 0x2) = 5 <== PR
ioctl(5, KVM_CHECK_EXTENSION, 0x84) = 0
The hv_enabled variable is set as follows:
/* Assume we're using HV mode when the HV module is loaded */
int hv_enabled = kvmppc_hv_ops ? 1 : 0;
if (kvm) {
/*
* Hooray - we know which VM type we're running on. Depend on
* that rather than the guess above.
*/
hv_enabled = is_kvmppc_hv_enabled(kvm);
}
so we're good. :)
The last sentence in the commit message is maybe^wprobably not comprehensive
enough...
What about the following ?
The hv_enabled variable is initialized to 1 if HV is loaded or 0 otherwise.
In the case KVM_CHECK_EXTENSION is used with a VM fd, hv_enabled is updated
to is_kvmppc_hv_enabled(kvm). Let's use it here, like everywhere else in this
function.
> > ---
> > arch/powerpc/kvm/powerpc.c | 3 +--
> > 1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> > index 3480faaf1ef8..ee279c7f4802 100644
> > --- a/arch/powerpc/kvm/powerpc.c
> > +++ b/arch/powerpc/kvm/powerpc.c
> > @@ -644,8 +644,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> > break;
> > #endif
> > case KVM_CAP_PPC_HTM:
> > - r = cpu_has_feature(CPU_FTR_TM_COMP) &&
> > - is_kvmppc_hv_enabled(kvm);
> > + r = cpu_has_feature(CPU_FTR_TM_COMP) && hv_enabled;
> > break;
> > default:
> > r = 0;
> >
>
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