Re: [Qemu-devel] [Qemu-block] [PATCH] scsi-generic: prevent guest from exceeding SG_IO limits

[Daniel P . Berrangé]

On Thu, Apr 18, 2019 at 12:47:37PM +0200, Kevin Wolf wrote:
> Am 18.04.2019 um 11:48 hat Paolo Bonzini geschrieben:
> > On 17/04/19 14:30, Stefan Hajnoczi wrote:
> > > On Wed, Apr 17, 2019 at 12:54 PM Paolo Bonzini <address@hidden> wrote:
> > >> Linux places a limit of UIO_MAXIOV pages on SG_IO ioctls (and if the 
> > >> limit
> > >> is exceeded, a confusing ENOMEM error is returned[1]).  Prevent the guest
> > >> from exceeding these limits, by capping the maximum transfer length to
> > >> that value in the block limits VPD page.
> > >>
> > >> [1] Oh well, at least it was easier to follow the kernel source knowing
> > >>     it had to end as ENOMEM...
> > >>
> > >> Cc: address@hidden
> > >> Cc: address@hidden
> > >> Cc: Stefan Hajnoczi <address@hidden>
> > >> Signed-off-by: Paolo Bonzini <address@hidden>
> > >> ---
> > >>  hw/scsi/scsi-generic.c | 17 +++++++++++++----
> > >>  1 file changed, 13 insertions(+), 4 deletions(-)
> > > 
> > > Reviewed-by: Stefan Hajnoczi <address@hidden>
> > > 
> > 
> > This is acually only an issue with kernels prior to 4.5, so it should be
> > fixed downstream instead.
> 
> I don't think that upstream QEMU has kernels > 4.5 as an official
> requirement, though? We try to be compatible with quite old libs, so we
> should stay compatible with old kernels, too.

We've not explicitly stated or checked a min kernel version, but our
min kernel is defined implicitly by our targetted build platforms:

  https://qemu.weilnetz.de/doc/qemu-doc.html#Supported-build-platforms

The oldest Linux distro under those rules is RHEL-7 (3.10.0), since
Debian Jessie actually updates its kernel version so is already on
version 4.5


Regards,
Daniel
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