Re: [PATCH v2] memblock: don't allocate new reserve_mem regions on a KHO boot

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] memblock: missing is_kho_boot() stub breaks tools/testing/memblock build
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commit 19549caf363a437d6178ec835c2f8f9d0ecc7f1d
Author: Jose A. Perez de Azpillaga <azpijr@gmail.com>

memblock: don't allocate new reserve_mem regions on a KHO boot

This patch rejects allocating new reserve_mem regions during a KHO boot
when the region cannot be revived from the previous kernel, returning
-EOPNOTSUPP instead of allocating from KHO_NOPRSRV memory.

> diff --git a/mm/memblock.c b/mm/memblock.c
> index a450092a80fb5..e325e0542c9a8 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -2827,7 +2827,16 @@ static int __init reserve_mem(char *p)
>  	if (reserve_mem_kho_revive(name, size, align))
>  		return 1;
>  
> -	/* TODO: Allocation must be outside of KHO_NOPRSRV region */
> +	/*
> +	 * On a KHO boot memblock only allocates from KHO_NOPRSRV memory here,
> +	 * which includes the bootmem the next kernel boots out of. Only regions
> +	 * handed over by the previous kernel are supported.
> +	 */
> +	if (is_kho_boot()) {
> +		pr_err("reserve_mem: can't allocate \"%s\" on a KHO boot\n", name);
> +		return -EOPNOTSUPP;
> +	}

[Severity: Low]
Does calling is_kho_boot() in reserve_mem() break the user-space memblock
test suite build in tools/testing/memblock?

When building tools/testing/memblock, mm/memblock.c is compiled with -I.
before -I../../include and without CONFIG_KEXEC_HANDOVER defined. As a
result, #include <linux/kexec_handover.h> resolves to the empty stub header
in tools/testing/memblock/linux/kexec_handover.h rather than
include/linux/kexec_handover.h:

tools/testing/memblock/linux/kexec_handover.h:
    #ifndef LINUX_KEXEC_HANDOVER_H
    #define LINUX_KEXEC_HANDOVER_H

    /*
     * Header stub to avoid test build breakage; we don't need to actually implement
     * any KHO functions as they are not used in the tests.
     */
    #endif /* LINUX_KEXEC_HANDOVER_H */

Other KHO helpers called unconditionally from mm/memblock.c, such as
kho_bootmem_overlap(), have stubs in tools/testing/memblock/internal.h:

tools/testing/memblock/internal.h:
    static inline bool kho_bootmem_overlap(phys_addr_t phys, size_t size)
    {
            return false;
    }

Should a stub for is_kho_boot() be added to tools/testing/memblock as well?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261104204235.9066-1-azpijr@gmail.com?part=1