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Re: [PATCH 4/7] x86/kexec: Support non-page-aligned kexec segments
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Kevin Lampis <kevin.lampis@xxxxxxxxxx>
- Date: Mon, 15 Jun 2026 18:43:25 +0000
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- Cc: "jbeulich@xxxxxxxx" <jbeulich@xxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- Delivery-date: Mon, 15 Jun 2026 18:43:37 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH 4/7] x86/kexec: Support non-page-aligned kexec segments
>It's startup_32 not startup32. Yet we hand over in 64bit mode, so why
>is startup_32 relevant rather than startup_64?
Probably just careless wording. I don't think it was the author's
intention to draw a distinction between 32 and 64.
>I can't find any hard alignment restriction (beyond 4k). There is a
>check involving BP_kernel_alignment, which is set to 2M, which makes
>sense; it's the alignment we set Xen to too.
>So, what's the real bug/problem here?
For normal kexec the userspace tools chop off the first part of the
kernel so everything aligns correctly.
For Secure Boot we need to load the whole kernel unmodified to pass
the signature check and that means the startup function is not aligned
correctly anymore.
We also changed the userspace tools to add padding to the start of the
kernel segment so the startup function is pushed out to the next 2M
byte boundary. So Secure Boot kexec does still work without this patch.
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