linux-kernel - Re: [PATCH v4 02/24] powerpc/pseries: Fix alignment of PLPKS structures and buffers

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Date:   Fri, 27 Jan 2023 14:20:37 +1100
From:   Andrew Donnellan <ajd@...ux.ibm.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "'Segher Boessenkool'" <segher@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     "gjoyce@...ux.ibm.com" <gjoyce@...ux.ibm.com>,
        "erichte@...ux.ibm.com" <erichte@...ux.ibm.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "nayna@...ux.ibm.com" <nayna@...ux.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "zohar@...ux.ibm.com" <zohar@...ux.ibm.com>,
        "sudhakar@...ux.ibm.com" <sudhakar@...ux.ibm.com>,
        "ruscur@...sell.cc" <ruscur@...sell.cc>,
        "joel@....id.au" <joel@....id.au>,
        "bgray@...ux.ibm.com" <bgray@...ux.ibm.com>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "gcwilson@...ux.ibm.com" <gcwilson@...ux.ibm.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v4 02/24] powerpc/pseries: Fix alignment of PLPKS
 structures and buffers

On Thu, 2023-01-26 at 17:31 +0000, David Laight wrote:
> Changing the size to kzalloc() doesn't help.
> The alignment depends on the allocator and is only required to have
> a relatively small alignment (ARCH_MINALIGN?) regardless of the size.
> 
> IIRC one of the allocators adds a small header to every item.
> It won't return 16 byte aligned items at all.

I'm relying on the behaviour described in Documentation/core-
api/memory-allocation.rst:

    The address of a chunk allocated with kmalloc is aligned to at
    least ARCH_KMALLOC_MINALIGN bytes. For sizes which are a power of
    two, the alignment is also guaranteed to be at least the respective
    size.

Is this wrong?


Andrew

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@...ux.ibm.com   IBM Australia Limited