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Re: [PATCH][4.17] EFI: don't convert memory marked for runtime use to ordinary RAM
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 4 Oct 2022 12:23:23 +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: Tue, 04 Oct 2022 10:23:33 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 04.10.2022 11:33, Roger Pau Monné wrote:
> On Tue, Oct 04, 2022 at 10:06:36AM +0200, Jan Beulich wrote:
>> On 30.09.2022 16:28, Roger Pau Monné wrote:
>>> On Fri, Sep 30, 2022 at 09:50:40AM +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 hence that type's handling can be left alone.
>>>
>>> What about dom0? Should it be translated to E820_RESERVED so that
>>> dom0 doesn't try to use it either?
>>
>> I'm afraid I don't understand the questions. Not the least because I
>> think "it" can't really mean "dom0" from the earlier sentence.
>
> Sorry, let me try again:
>
> The memory map provided to dom0 will contain E820_ACPI entries for
> memory ranges with the EFI_MEMORY_RUNTIME attributes in the EFI memory
> map. Is there a risk from dom0 reclaiming such E820_ACPI ranges,
> overwriting the data needed for runtime services?
How would Dom0 go about doing so? It has no control over what we hand
to the page allocator - it can only free pages which were actually
allocated to it. E820_ACPI and E820_RESERVED pages are assigned to
DomIO - Dom0 can map and access them, but it cannot free them.
Jan
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