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Re: [XEN v3] Xen: Ensure "xenheap_bits - PAGE_SHIFT" can be used as a rhs operand of shift operator
- To: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 2 Dec 2022 14:43:56 +0100
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- Delivery-date: Fri, 02 Dec 2022 13:44:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.12.2022 13:35, Ayan Kumar Halder wrote:
> We want to ensure that "xenheap_bits - PAGE_SHIFT" is strictly less than
> the number of bits to represent unsigned long as it is used a rhs operand
> to shift mfn.
> It is also important to note that the "xenheap_bits - PAGE_SHIFT" is never
> used to shift an address (rather than a frame number), and going forward
> then also shouldn't be (perhaps unless further precautions are taken).
Hmm, now you've lost why you are making the change in the first place:
The way things are before the patch is quite fine for the described
purpose. (This then also extends to the title. I should have noticed
this in v2 already, but didn't because I still had the v1 title in mind.)
Furthermore in the 2nd paragraph instead of 'the "xenheap_bits -
PAGE_SHIFT"' you mean '"xenheap_bits" alone'.
Jan
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