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Re: [PATCH 1/1] xen/efi: Config parsing: Free the same page count as allocated.
- To: Bernhard Kaindl <bernhard.kaindl@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 22 Apr 2026 12:48:29 +0200
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- Cc: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>
- Delivery-date: Wed, 22 Apr 2026 10:48:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 22.04.2026 10:46, Bernhard Kaindl wrote:
> Jan Beulich wrote at 10:20:
>> On 22.04.2026 08:48, Jan Beulich wrote:
>>
>>> As indicated above, I'm not convinced though that we really want to
>>> alter file->size. I'd instead add 1 in the few instances of
>>> "efi_bs->FreePages(cfg.addr, PFN_UP(cfg.size))". Sadly the adding of 1
>>> is conditional in read_section(), so maybe a "need_to_increment"
>>> boolean wants adding next to the need_to_free one? Then a small helper
>>> function may be warranted for those few instances of freeing cfg.addr.
>>
>> Actually, no separate flag looks to be needed. If for the cfg file we set
>> ->need_to_free, we know we allocated the one extra byte.
>
> No, also cfg->need_to_free is always set when AllocatePages was successful,
> xen/common/efi/boot.c, read_file(), lines 862 to 867:
>
> ret = efi_bs->AllocatePages(AllocateMaxAddress, EfiLoaderData,
> PFN_UP(size + (file == &cfg)), &file->addr);
> if ( EFI_ERROR(ret) )
> goto fail;
>
> file->need_to_free = true;
Of course. And for the cfg file (and only that) it means there's one more
byte allocated. So cfg file buffer freeing can uniformly add 1.
Jan
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