linux-kernel - Re: [PATCH v2 03/13] kho: Introduce high-level memory allocation API

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Message-ID: <20251116064918.35549-1-ioworker0@gmail.com>
Date: Sun, 16 Nov 2025 14:49:18 +0800
From: Lance Yang <ioworker0@...il.com>
To: pasha.tatashin@...een.com
Cc: akpm@...ux-foundation.org,
	arnd@...db.de,
	bhe@...hat.com,
	coxu@...hat.com,
	dave@...ilevsky.ca,
	ebiggers@...gle.com,
	graf@...zon.com,
	jasonmiu@...gle.com,
	kees@...nel.org,
	kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	rppt@...nel.org,
	Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH v2 03/13] kho: Introduce high-level memory allocation API

From: Lance Yang <lance.yang@...ux.dev>


On Fri, 14 Nov 2025 13:59:52 -0500, Pasha Tatashin wrote:
> Currently, clients of KHO must manually allocate memory (e.g., via
> alloc_pages), calculate the page order, and explicitly call
> kho_preserve_folio(). Similarly, cleanup requires separate calls to
> unpreserve and free the memory.
> 
> Introduce a high-level API to streamline this common pattern:
> 
> - kho_alloc_preserve(size): Allocates physically contiguous, zeroed
>   memory and immediately marks it for preservation.
> - kho_unpreserve_free(ptr): Unpreserves and frees the memory
>   in the current kernel.
> - kho_restore_free(ptr): Restores the struct page state of
>   preserved memory in the new kernel and immediately frees it to the
>   page allocator.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> ---
>  include/linux/kexec_handover.h     | 22 +++++---
>  kernel/liveupdate/kexec_handover.c | 87 ++++++++++++++++++++++++++++++
>  2 files changed, 102 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
> index 80ece4232617..38a9487a1a00 100644
> --- a/include/linux/kexec_handover.h
> +++ b/include/linux/kexec_handover.h
> @@ -2,8 +2,9 @@
>  #ifndef LINUX_KEXEC_HANDOVER_H
>  #define LINUX_KEXEC_HANDOVER_H
>  
> -#include <linux/types.h>
> +#include <linux/err.h>
>  #include <linux/errno.h>
> +#include <linux/types.h>
>  
>  struct kho_scratch {
>  	phys_addr_t addr;
> @@ -48,6 +49,9 @@ int kho_preserve_pages(struct page *page, unsigned int nr_pages);
>  int kho_unpreserve_pages(struct page *page, unsigned int nr_pages);
>  int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation);
>  int kho_unpreserve_vmalloc(struct kho_vmalloc *preservation);
> +void *kho_alloc_preserve(size_t size);
> +void kho_unpreserve_free(void *mem);
> +void kho_restore_free(void *mem);
>  struct folio *kho_restore_folio(phys_addr_t phys);
>  struct page *kho_restore_pages(phys_addr_t phys, unsigned int nr_pages);
>  void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);
> @@ -101,6 +105,14 @@ static inline int kho_unpreserve_vmalloc(struct kho_vmalloc *preservation)
>  	return -EOPNOTSUPP;
>  }
>  
> +void *kho_alloc_preserve(size_t size)
> +{
> +	return ERR_PTR(-EOPNOTSUPP);
> +}
> +
> +void kho_unpreserve_free(void *mem) { }
> +void kho_restore_free(void *mem) { }

The compile is unhapply here when CONFIG_KEXEC_HANDOVER is not set ...

```
ld: arch/x86/realmode/rm/video-mode.o: in function `kho_alloc_preserve':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:102: multiple definition of `kho_alloc_preserve'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:102: first defined here
ld: arch/x86/realmode/rm/video-mode.o: in function `kho_unpreserve_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:104: multiple definition of `kho_unpreserve_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:104: first defined here
ld: arch/x86/realmode/rm/video-mode.o: in function `kho_restore_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:105: multiple definition of `kho_restore_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:105: first defined here
ld: arch/x86/realmode/rm/regs.o: in function `kho_alloc_preserve':
/home/runner/work/mm-test-robot/mm-test-robot/linux/arch/x86/realmode/rm/regs.c:102: multiple definition of `kho_alloc_preserve'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:102: first defined here
ld: arch/x86/realmode/rm/regs.o: in function `kho_unpreserve_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/arch/x86/realmode/rm/regs.c:104: multiple definition of `kho_unpreserve_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:104: first defined here
ld: arch/x86/realmode/rm/regs.o: in function `kho_restore_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/arch/x86/realmode/rm/regs.c:105: multiple definition of `kho_restore_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:105: first defined here
ld: arch/x86/realmode/rm/video-vga.o: in function `kho_alloc_preserve':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:102: multiple definition of `kho_alloc_preserve'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:102: first defined here
ld: arch/x86/realmode/rm/video-vga.o: in function `kho_unpreserve_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:104: multiple definition of `kho_unpreserve_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:104: first defined here
ld: arch/x86/realmode/rm/video-vga.o: in function `kho_restore_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:105: multiple definition of `kho_restore_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:105: first defined here
ld: arch/x86/realmode/rm/video-vesa.o: in function `kho_alloc_preserve':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:102: multiple definition of `kho_alloc_preserve'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:102: first defined here
ld: arch/x86/realmode/rm/video-vesa.o: in function `kho_unpreserve_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:104: multiple definition of `kho_unpreserve_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:104: first defined here
ld: arch/x86/realmode/rm/video-vesa.o: in function `kho_restore_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:105: multiple definition of `kho_restore_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:105: first defined here
ld: arch/x86/realmode/rm/video-bios.o: in function `kho_alloc_preserve':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:102: multiple definition of `kho_alloc_preserve'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:102: first defined here
ld: arch/x86/realmode/rm/video-bios.o: in function `kho_unpreserve_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:104: multiple definition of `kho_unpreserve_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:104: first defined here
ld: arch/x86/realmode/rm/video-bios.o: in function `kho_restore_free':
/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:105: multiple definition of `kho_restore_free'; arch/x86/realmode/rm/wakemain.o:/home/runner/work/mm-test-robot/mm-test-robot/linux/./include/linux/kexec_handover.h:105: first defined here
make[5]: *** [arch/x86/realmode/rm/Makefile:49: arch/x86/realmode/rm/realmode.elf] Error 1
make[4]: *** [arch/x86/realmode/Makefile:22: arch/x86/realmode/rm/realmode.bin] Error 2
make[3]: *** [scripts/Makefile.build:556: arch/x86/realmode] Error 2
```

Perhaps these stubs should be declared as static inline? That should make
the compiler happy and resolve the linking errors :)

----8<----
diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index 6dd0dcdf0ec1..5f7b9de97e8d 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -96,13 +96,13 @@ static inline int kho_preserve_vmalloc(void *ptr,

 static inline void kho_unpreserve_vmalloc(struct kho_vmalloc *preservation) { }

-void *kho_alloc_preserve(size_t size)
+static inline void *kho_alloc_preserve(size_t size)
 {
        return ERR_PTR(-EOPNOTSUPP);
 }

-void kho_unpreserve_free(void *mem) { }
-void kho_restore_free(void *mem) { }
+static inline void kho_unpreserve_free(void *mem) { }
+static inline void kho_restore_free(void *mem) { }

 static inline struct folio *kho_restore_folio(phys_addr_t phys)
 {
---

[...]

Cheers,
Lance