Re: [Xen-devel] disable qemu PCI devices in HVM domains

[Steven Smith <steven.smith@xxxxxxxxxxxxx>]

> > > +#ifndef CONFIG_STUBDOM
> > > +        /* Invalidate buffer cache for this device. */
> > > +        ioctl(s->fd, BLKFLSBUF, 0);
> > > +#endif
> ...
> > So this hunk is probably, strictly speaking, redundant for all current
> > driver implementations.
> 
> Right, good.
> 
> > Having said that, it's clearly more robust to not rely on the various
> > drivers being able to get in before any writes are issued, so it's
> > probably a good thing to have anyway.
> 
> Well, except that I would prefer not to carry a change in this part of
> the qemu code unless it was actually necessary.
It's obviously always good to reduce skew with upstream, but in this
particular case it's a relatively small patch which eliminates a class
of potential bugs which are:

-- Nasty, in that they could lead to stuff on disk becoming corrupt.
-- Likely to be hard to reliably reproduce.
-- Difficult to demonstrate to be absent in all cases, because it's
   hard to be absolutely confident that the Windows bootloader doesn't
   write *something* under some obscure situation which we haven't
   thought of.

Personally, I'd feel a lot more confident with the flush present, but
if you really hate it then it can probably go.

Steven.

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