Re: [PATCH v10] Preserve the EFI System Resource Table for dom0

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.07.2022 01:14, Demi Marie Obenour wrote:
> The EFI System Resource Table (ESRT) is necessary for fwupd to identify
> firmware updates to install.  According to the UEFI specification §23.4,
> the ESRT shall be stored in memory of type EfiBootServicesData.  However,
> memory of type EfiBootServicesData is considered general-purpose memory
> by Xen, so the ESRT needs to be moved somewhere where Xen will not
> overwrite it.  Copy the ESRT to memory of type EfiRuntimeServicesData,
> which Xen will not reuse.  dom0 can use the ESRT if (and only if) it is
> in memory of type EfiRuntimeServicesData.
> 
> Earlier versions of this patch reserved the memory in which the ESRT was
> located.  This created awkward alignment problems, and required either
> splitting the E820 table or wasting memory.  It also would have required
> a new platform op for dom0 to use to indicate if the ESRT is reserved.
> By copying the ESRT into EfiRuntimeServicesData memory, the E820 table
> does not need to be modified, and dom0 can just check the type of the
> memory region containing the ESRT.  The copy is only done if the ESRT is
> not already in EfiRuntimeServicesData memory, avoiding memory leaks on
> repeated kexec.
> 
> See https://lore.kernel.org/xen-devel/20200818184018.GN1679@mail-itl/T/
> for details.
> 
> Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
> Tested-by: Luca Fancellu <luca.fancellu@xxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>