On Tue, 9 Jan 2024 at 16:31, Peter Maydell <[email protected]> wrote:
>
> On Tue, 9 Jan 2024 at 16:24, Michael Tokarev <[email protected]> wrote:
> >
> > 09.01.2024 16:52, Peter Maydell:
> > ..
> > > Oh, your kernel isn't an LPAE one (i.e. CONFIG_LPAE is not
> > > set). That will obviously never be able to access registers
> > > above the 4GB mark (though the kernel's error message in this
> > > situation is a bit unhelpful and could perhaps be improved).
> > > If I set CONFIG_LPAE on the non-working config it starts working.
> > >
> > > I think then the answer is:
> > > * if you want to use the (default) highmem setup, use an LPAE kernel
> > > * if you want to use a non-LPAE kernel, tell QEMU to avoid
> > > highmem using '-machine virt,highmem=off'
> > >
> > > It was just a bug that we were accidentally disabling highmem
> > > for the 32-bit 'max' CPU before b8f7959f28c4f3.
> >
> > Wow wow wow. So it's a pebkac bug, not qemu bug.. :)
> > I didn't even know about LPAE before this email, and knew very
> > little about arm stuff too.
> >
> > Thank you very much for your work and time!
> >
> > The diagnostics here is definitely.. "interesting", so to say, it's
> > very "obvious" what the problem is.. from the kernel messages :)
>
> Yeah. I don't personally have the time to try to follow up
> on improving the kernel handling of this, but if anybody else
> does, I think the problem is that the function __of_address_to_resource()
> which fills in a 'struct resource' from a DTB entry silently
> truncates over-large values when it fills in r->start and r->end
> (which are of type phys_addr_t, and so only 32 bits on non-LPAE
> kernels). So that function seems like a good place to put some
>
> if (taddr or taddr + size are above 4GB) {
> warn("resource foo is too high in the address space to use
> (did you forget to enable CONFIG_LPAE?)\n");
> return -EINVAL;
> }
>
> type handling which would then catch this user error relatively
> comprehensibly for most devices.
...and the less pseudocodey version of that probably looks
like the similar check in of_pci_range_to_resource(), viz
if (sizeof(resource_size_t) < 8) &&
(upper_32_bits(taddr) || upper_32_bits(taddr + size)) {
...
}
-- PMM
