Re: [PATCH v3] iscsi_ibft: Fix finding the iBFT under Xen Dom 0

From: Konrad Rzeszutek Wilk <konrad@darnok.org>
To: Juergen Gross <jgross@suse.com>
Cc: Ross Lagerwall <ross.lagerwall@citrix.com>,
	LKML <linux-kernel@vger.kernel.org>,
	 xen-devel@lists.xenproject.org, Jan Beulich <jbeulich@suse.com>,
	 Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	 Dave Hansen <dave.hansen@linux.intel.com>,
	X86 ML <x86@kernel.org>,
	 Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Peter Jones <pjones@redhat.com>,
	 Konrad Rzeszutek Wilk <konrad@kernel.org>
Subject: Re: [PATCH v3] iscsi_ibft: Fix finding the iBFT under Xen Dom 0
Date: Fri, 9 Jun 2023 11:22:48 -0400	[thread overview]
Message-ID: <CAPbh3ruFn1to+t9QiuYM7h8CqL-fs2q73Rscj6PWGZuBkS8FEw@mail.gmail.com> (raw)
In-Reply-To: <f2ccd563-4fac-084f-bd11-e6819dff5710@suse.com>

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Feel free to add my Acked-by.

Dave, are you OK with the change in where the reserve call is made?

Thx

On Fri, Jun 9, 2023, 11:08 AM Juergen Gross <jgross@suse.com> wrote:

> On 05.06.23 12:28, Ross Lagerwall wrote:
> > To facilitate diskless iSCSI boot, the firmware can place a table of
> > configuration details in memory called the iBFT. The presence of this
> > table is not specified, nor is the precise location (and it's not in the
> > E820) so the kernel has to search for a magic marker to find it.
> >
> > When running under Xen, Dom 0 does not have access to the entire host's
> > memory, only certain regions which are identity-mapped which means that
> > the pseudo-physical address in Dom0 == real host physical address.
> > Add the iBFT search bounds as a reserved region which causes it to be
> > identity-mapped in xen_set_identity_and_remap_chunk() which allows Dom0
> > access to the specific physical memory to correctly search for the iBFT
> > magic marker (and later access the full table).
> >
> > This necessitates moving the call to reserve_ibft_region() somewhat
> > later so that it is called after e820__memory_setup() which is when the
> > Xen identity mapping adjustments are applied. The precise location of
> > the call is not too important so I've put it alongside dmi_setup() which
> > does similar scanning of memory for configuration tables.
> >
> > Finally in the iBFT find code, instead of using isa_bus_to_virt() which
> > doesn't do the right thing under Xen, use early_memremap() like the
> > dmi_setup() code does.
> >
> > The result of these changes is that it is possible to boot a diskless
> > Xen + Dom0 running off an iSCSI disk whereas previously it would fail to
> > find the iBFT and consequently, the iSCSI root disk.
> >
> > Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
>
> Reviewed-by: Juergen Gross <jgross@suse.com>
>
>
> Juergen
>
>

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