linux-kernel - Re: [PATCH v2 2/4] xen-pcifront: Align address of flags to size of unsigned long

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Date:   Tue, 26 Nov 2019 11:02:13 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Laight <David.Laight@...LAB.COM>,
        Ashok Raj <ashok.raj@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v2 2/4] xen-pcifront: Align address of flags to size of
 unsigned long

On 25.11.19 20:43, Fenghua Yu wrote:
> The address of "flags" is passed to atomic bitops which require the
> address is aligned to size of unsigned long.
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> ---
>   include/xen/interface/io/pciif.h | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/include/xen/interface/io/pciif.h b/include/xen/interface/io/pciif.h
> index d9922ae36eb5..639d5fb484a3 100644
> --- a/include/xen/interface/io/pciif.h
> +++ b/include/xen/interface/io/pciif.h
> @@ -103,8 +103,11 @@ struct xen_pcie_aer_op {
>   	uint32_t devfn;
>   };
>   struct xen_pci_sharedinfo {
> -	/* flags - XEN_PCIF_* */
> -	uint32_t flags;
> +	/* flags - XEN_PCIF_*. Force alignment for atomic bit operations. */
> +	union {
> +		uint32_t	flags;
> +		unsigned long	flags_alignment;
> +	};
>   	struct xen_pci_op op;
>   	struct xen_pcie_aer_op aer_op;
>   };
> 

NAK.

This is an interface definition for communication between Xen dom0 and
guests via shared memory. It can't be changed.

BTW: you should Cc: the maintainers for the files you are modifying.


Juergen