linux-kernel - Re: [PATCH v3 7/7] xen: tolerate ACPI NVS memory overlapping with Xen allocated memory

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Message-ID: <3fb809a5-d0a2-4b72-b810-13e4ee93b8b7@suse.com>
Date: Tue, 10 Sep 2024 14:36:47 +0200
From: Jan Beulich <jbeulich@...e.com>
To: Juergen Gross <jgross@...e.com>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org,
 Marek Marczykowski-Górecki
 <marmarek@...isiblethingslab.com>, linux-kernel@...r.kernel.org,
 x86@...nel.org
Subject: Re: [PATCH v3 7/7] xen: tolerate ACPI NVS memory overlapping with Xen
 allocated memory

On 10.09.2024 12:39, Juergen Gross wrote:
> In order to minimize required special handling for running as Xen PV
> dom0, the memory layout is modified to match that of the host. This
> requires to have only RAM at the locations where Xen allocated memory
> is living. Unfortunately there seem to be some machines, where ACPI
> NVS is located at 64 MB, resulting in a conflict with the loaded
> kernel or the initial page tables built by Xen.
> 
> Avoid this conflict by swapping the ACPI NVS area in the memory map
> with unused RAM. This is possible via modification of the dom0 P2M map.
> Accesses to the ACPI NVS area are done either for saving and restoring
> it across suspend operations (this will work the same way as before),
> or by ACPI code when NVS memory is referenced from other ACPI tables.
> The latter case is handled by a Xen specific indirection of
> acpi_os_ioremap().
> 
> While the E820 map can (and should) be modified right away, the P2M
> map can be updated only after memory allocation is working, as the P2M
> map might need to be extended.
> 
> Fixes: 808fdb71936c ("xen: check for kernel memory conflicting with memory layout")
> Signed-off-by: Juergen Gross <jgross@...e.com>
> Tested-by: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>

Reviewed-by: Jan Beulich <jbeulich@...e.com>