linux-kernel - Re: [PATCH 5/6] kho: Relocate vmalloc preservation structure to KHO ABI header

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Message-ID: <2vxz5x8wcdv3.fsf@kernel.org>
Date: Tue, 20 Jan 2026 18:56:16 +0000
From: Pratyush Yadav <pratyush@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Pratyush Yadav <pratyush@...nel.org>,  Andrew Morton
 <akpm@...ux-foundation.org>,  Alexander Graf <graf@...zon.com>,  Jason Miu
 <jasonmiu@...gle.com>,  Jonathan Corbet <corbet@....net>,  Pasha Tatashin
 <pasha.tatashin@...een.com>,  kexec@...ts.infradead.org,
  linux-doc@...r.kernel.org,  linux-kernel@...r.kernel.org,
  linux-mm@...ck.org
Subject: Re: [PATCH 5/6] kho: Relocate vmalloc preservation structure to KHO
 ABI header

On Tue, Jan 20 2026, Mike Rapoport wrote:

> On Tue, Jan 20, 2026 at 04:26:51PM +0000, Pratyush Yadav wrote:
>> On Mon, Jan 05 2026, Mike Rapoport wrote:
>> 
>> > From: Jason Miu <jasonmiu@...gle.com>
>> >
>> > The `struct kho_vmalloc` defines the in-memory layout for preserving
>> > vmalloc regions across kexec. This layout is a contract between kernels
>> > and part of the KHO ABI.
>> >
>> > To reflect this relationship, the related structs and helper macros are
>> > relocated to the ABI header, `include/linux/kho/abi/kexec_handover.h`.
>> > This move places the structure's definition under the protection of the
>> > KHO_FDT_COMPATIBLE version string.
>> >
>> > The structure and its components are now also documented within the
>> > ABI header to describe the contract and prevent ABI breaks.
>> >
>> > Signed-off-by: Jason Miu <jasonmiu@...gle.com>
>> > Co-developed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
>> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
>> [...]
>> > +/* Helper macro to define a union for a serializable pointer. */
>> > +#define DECLARE_KHOSER_PTR(name, type)	\
>> > +	union {                        \
>> > +		u64 phys;              \
>> > +		type ptr;              \
>> > +	} name
>> > +
>> > +/* Stores the physical address of a serializable pointer. */
>> > +#define KHOSER_STORE_PTR(dest, val)               \
>> > +	({                                        \
>> > +		typeof(val) v = val;              \
>> > +		typecheck(typeof((dest).ptr), v); \
>> > +		(dest).phys = virt_to_phys(v);    \
>> > +	})
>> > +
>> > +/* Loads the stored physical address back to a pointer. */
>> > +#define KHOSER_LOAD_PTR(src)						\
>> > +	({                                                                   \
>> > +		typeof(src) s = src;                                         \
>> > +		(typeof((s).ptr))((s).phys ? phys_to_virt((s).phys) : NULL); \
>> > +	})
>> 
>> Nit: not a fan of exposing code internals to the ABI header. But without
>> this the definition of kho_vmalloc_hdr won't make any sense to someone
>> reading the doc without looking at the code. Dunno if we can do anything
>> better though...
>
> These might be actually useful for other KHO users. 

Hmm, okay. Let's keep them here then.

[...]

-- 
Regards,
Pratyush Yadav