Re: [PATCH 3/3] x86/PCI: limit the size of the 64bit BAR to 256GB

[Christian KÃnig]

Am 08.12.2017 um 18:56 schrieb Bjorn Helgaas:
> On Wed, Dec 06, 2017 at 01:51:18PM -0600, Bjorn Helgaas wrote:
> > On Wed, Nov 29, 2017 at 03:12:29PM +0100, Christian KÃnig wrote:
> > > This avoids problems with Xen which hides some memory resources from the
> > > OS and potentially also allows memory hotplug while this fixup is
> > > enabled.
> > The patch itself is OK, but the changelog doesn't say enough about
> > what the problem is.  I have no clue about what the Xen issue is or
> > why limiting the BAR to 256GB avoids the problem or what this has to
> > do with memory hotplug.
> >
> > For example, we should be able to tell why 256GB is the right number.
> > Maybe there's something specific in Xen you can reference?  Maybe an
> > example of what goes wrong with some details?
> Ping?

Sorry for the delay, first been to busy and then got a bad cold and 
today is the first day I've got out of bed again.

> Is this change required to fix issues people are seeing?  If
> so, we either need to rework the changelog and get it merged, or
> revert the quirk as a whole.

It's just a precaution to eventually avoid problems, I will try to 
provided a patch with updated commit log tomorrow.

> I tentatively applied the first two patches to for-linus, but I
> haven't asked Linus to pull them because I assumed we really needed
> all three.

The first two patches are perfectly enough for now.

Thanks,
Christian.

> Bjorn
>
> > > Signed-off-by: Christian KÃnig <christian.koenig@xxxxxxx>
> > > ---
> > >   arch/x86/pci/fixup.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c
> > > index c817ab85dc82..149adbc7f2a3 100644
> > > --- a/arch/x86/pci/fixup.c
> > > +++ b/arch/x86/pci/fixup.c
> > > @@ -701,7 +701,7 @@ static void pci_amd_enable_64bit_bar(struct pci_dev *dev)
> > >   	res->name = "PCI Bus 0000:00";
> > >   	res->flags = IORESOURCE_PREFETCH | IORESOURCE_MEM |
> > >   		IORESOURCE_MEM_64 | IORESOURCE_WINDOW;
> > > -	res->start = 0x100000000ull;
> > > +	res->start = 0xbd00000000ull;
> > >   	res->end = 0xfd00000000ull - 1;
> > >   
> > >   	/* Just grab the free area behind system memory for this */
> > > --
> > > 2.11.0