[PATCH v2 00/19] mm: Support huge pfnmaps

[Jason Gunthorpe]

On Wed, Sep 04, 2024 at 09:38:22AM -0700, Jiaqi Yan wrote:
> On Wed, Sep 4, 2024 at 8:52 AM Jason Gunthorpe <jgg at nvidia.com> wrote:
> >
> > On Thu, Aug 29, 2024 at 12:21:39PM -0700, Jiaqi Yan wrote:
> >
> > > I think we still want to attempt to SIGBUS userspace, regardless of
> > > doing unmap_mapping_range or not.
> >
> > IMHO we need to eliminate this path if we actually want to keep things
> > mapped.
> >
> > There is no way to generate the SIGBUS without poking a 4k hole in the
> > 1G page, as only that 4k should get SIGBUS, every other byte of the 1G
> > is clean.
> 
> Ah, sorry I wasn't clear. The SIGBUS will be only for poisoned PFN;
> clean PFNs under the same PUD/PMD for sure don't need any SIGBUS,
> which is the whole purpose of not unmapping.

You can't get a SIGBUS if the things are still mapped. This is why the
SIGBUS flow requires poking a non-present hole around the poisoned
memory.

So keeping things mapped at 1G also means giving up on SIGBUS.

Jason