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Re: [PATCH v2][4.17] EFI: don't convert memory marked for runtime use to ordinary RAM
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 6 Oct 2022 11:51:10 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>
- Delivery-date: Thu, 06 Oct 2022 09:51:28 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu, Oct 06, 2022 at 10:58:43AM +0200, Jan Beulich wrote:
> On 06.10.2022 10:53, Roger Pau Monné wrote:
> > On Thu, Oct 06, 2022 at 10:40:56AM +0200, Jan Beulich wrote:
> >> efi_init_memory() in both relevant places is treating EFI_MEMORY_RUNTIME
> >> higher priority than the type of the range. To avoid accessing memory at
> >> runtime which was re-used for other purposes, make
> >> efi_arch_process_memory_map() follow suit. While on x86 in theory the
> >> same would apply to EfiACPIReclaimMemory, we don't actually "reclaim"
> >> E820_ACPI memory there (and it would be a bug if the Dom0 kernel tried
> >> to do so, bypassing Xen's memory management), hence that type's handling
> >
> > Strictly speaking I don't think dom0 needs to bypass Xen's memory
> > management, just overwriting the page would be bad enough for runtime
> > services to not work correctly I would think.
>
> Then how about:
>
> "While on x86 in theory the same would apply to EfiACPIReclaimMemory, we don't
> actually "reclaim" or clobber E820_ACPI memory there (and it would be a bug
> if
> the Dom0 kernel tried to reclaim the range, bypassing Xen's memory
> management,
> plus it would be at least bogus if it clobbered that space), hence that
> type's
> handling can be left alone."
>
> I didn't think the clobbering aspect needed pointing out, as the same applies
> to all other memory which Dom0 is able to access beyond its actual allocation.
I think it makes it clear that just clobbering it from dom0 could
cause issues to runtime services. I guess it can be extrapolated that
clobbering is also bad if reclaiming is.
Thanks, Roger.
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