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Re: [PATCH 05/12] x86/boot: move headroom to boot modules
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 6 Nov 2024 19:50:02 -0500
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- Delivery-date: Thu, 07 Nov 2024 00:50:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 11/6/24 18:00, Andrew Cooper wrote:
On 02/11/2024 5:25 pm, Daniel P. Smith wrote:
diff --git a/xen/arch/x86/include/asm/bootinfo.h
b/xen/arch/x86/include/asm/bootinfo.h
index b1549d8c8f93..e337baa905f0 100644
--- a/xen/arch/x86/include/asm/bootinfo.h
+++ b/xen/arch/x86/include/asm/bootinfo.h
@@ -30,6 +30,28 @@ struct boot_module {
enum bootmod_type type;
+ /*
+ * A boot module may need decompressing by Xen. Headroom is an estimate of
+ * the additional space required to decompress the module.
+ *
+ * Headroom is accounted for at the start of the module. Decompressing is
+ * done in-place with input=start, output=start-headroom, expecting the
+ * pointers to become equal (give or take some rounding) when decompression
+ * is complete.
+ *
+ * Memory layout at boot:
+ *
+ * start ----+
+ * v
+ * |<-----headroom------>|<------size------->|
+ * +-------------------+
+ * | Compressed Module |
+ * +---------------------+-------------------+
+ * | Decompressed Module |
+ * +-----------------------------------------+
+ */
+ unsigned long headroom;
+
/*
* Module State Flags:
* relocated: indicates module has been relocated in memory.
By the end of the series, this ends very poorly laid out.
It works a whole lot better when putting the bitfields between type and
headroom.
Ack.
Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Thanks.
v/r,
dps
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