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Re: Arm: AArch32: Need suggestions to support 32 bit physical addresses
- To: Ayan Kumar Halder <ayankuma@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 30 Nov 2022 13:01:57 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, "Stabellini, Stefano" <stefano.stabellini@xxxxxxx>, bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Andre Przywara <andre.przywara@xxxxxxx>, "Volodymyr_Babchuk@xxxxxxxx" <Volodymyr_Babchuk@xxxxxxxx>, Rahul Singh <rahul.singh@xxxxxxx>, Vladimir Murzin <vladimir.murzin@xxxxxxx>, Julien Grall <julien@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 30 Nov 2022 12:02:05 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.11.2022 12:27, Ayan Kumar Halder wrote:
> Looking at "min(flsl(mfn + 1) - 1 + PAGE_SHIFT, PADDR_BITS);", I do not
> understand the reason for "... -1" (ie subtracting by 1).
>
> Do you know the reason ?
That's because fls() and flsl() and friends return 1-based bit indexes
(with 0 being returned when the input was zero), when we need 0-based
values here.
Jan
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