Re: [PATCH v2] iscsi_ibft: Fix finding the iBFT under Xen Dom 0

[Juergen Gross <jgross@xxxxxxxx>]

On 01.06.23 18:57, Dave Hansen wrote:
> On 5/30/23 08:01, Ross Lagerwall wrote:
> > Since firmware doesn't indicate the iBFT in the E820, add a reserved
> > region so that it gets identity mapped when running as Dom 0 so that it
> > is possible to search for it. Move the call to reserve_ibft_region()
> > later so that it is called after the Xen identity mapping adjustments
> > are applied.
> >
> > Finally, instead of using isa_bus_to_virt() which doesn't do the right
> > thing under Xen, use early_memremap() like the dmi_scan code does.
> This is connecting Xen, iSCSI and x86.  Some background here would be
> *really* nice for dummies like me that deal heavily in only one of those
> three.
>
> One or two sentences like this:
>
>         Firmware can provide an iSCSI-specific table called the iBFT
>         which helps the OS boot from iSCSI devices.
>
> can go a long way for dummies like me.  As could some background about
> why this:
>
>         ... add a reserved region so that it gets identity mapped when
>         running as Dom 0 so that it is possible to search for it.
>
> These are all English words, but off the top of my head, I have no idea
> why reserved regions get identity mapped when running as Dom 0 or why
> that makes it possible to search.
>
> The addresses and size here:
>
> > +#ifdef CONFIG_ISCSI_IBFT_FIND
> > +               /* Reserve 0.5 MiB to 1 MiB region so iBFT can be found */
> > +               xen_e820_table.entries[xen_e820_table.nr_entries].addr = 
> > 0x80000;
> > +               xen_e820_table.entries[xen_e820_table.nr_entries].size = 
> > 0x80000;
> > +               xen_e820_table.entries[xen_e820_table.nr_entries].type = 
> > E820_TYPE_RESERVED;
> > +               xen_e820_table.nr_entries++;
> > +#endif
> also appear to be conjured out of thin air.
I'd suggest to move the definitions of IBFT_START and IBFT_END from
drivers/firmware/iscsi_ibft_find.c to include/linux/iscsi_ibft.h and use
them here.


Juergen

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