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Re: [PATCH 1/3] x86/boot: Explain how moving mod[0] works
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Mon, 29 Apr 2024 14:49:37 -0400
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- Cc: Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Daniel Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>, Christopher Clark <christopher.w.clark@xxxxxxxxx>
- Delivery-date: Mon, 29 Apr 2024 18:49:53 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2024-04-26 10:01, Andrew Cooper wrote:
modules_headroom is a misleading name as it applies strictly to mod[0] only,
and the movement loop is deeply unintuitive and completely undocumented.
Provide help to whomever needs to look at this code next.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Daniel Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
CC: Christopher Clark <christopher.w.clark@xxxxxxxxx>
---
xen/arch/x86/setup.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index caf235c6286d..59907fae095f 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1432,6 +1432,11 @@ void asmlinkage __init noreturn __start_xen(unsigned
long mbi_p)
/* Is the region suitable for relocating the multiboot modules? */
for ( j = mbi->mods_count - 1; j >= 0; j-- )
{
+ /*
+ * 'headroom' is a guess for the decompressed size and
+ * decompressor overheads of mod[0] (the dom0 kernel). When we
+ * move mod[0], we incorperate this as extra space at the start.
incorporate
With that:
Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxxxx>
Thanks,
Jason
+ */
unsigned long headroom = j ? 0 : modules_headroom;
unsigned long size = PAGE_ALIGN(headroom + mod[j].mod_end);
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