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Re: [PATCH 1/7] xen/arm32: head: Add missing isb in setup_fixmap()
- To: Julien Grall <julien@xxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Tue, 4 Jul 2023 14:53:04 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Luca Fancellu <Luca.Fancellu@xxxxxxx>, "michal.orzel@xxxxxxx" <michal.orzel@xxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Tue, 04 Jul 2023 14:53:38 +0000
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- Thread-topic: [PATCH 1/7] xen/arm32: head: Add missing isb in setup_fixmap()
Hi Julien,
> On 19 Jun 2023, at 19:01, Julien Grall <julien@xxxxxxx> wrote:
>
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> Per the Arm Arm (ARM DDI 0406C.d A3.8.3):
>
> "The DMB and DSB memory barriers affect reads and writes to the memory
> system generated by load/store instructions and data or unified cache
> maintenance operations being executed by the processor. Instruction
> fetches or accesses caused by a hardware translation table access are
> not explicit accesses."
>
> In setup_fixmap(), we write the fixmap area and may be used soon after,
> for instance, to write to the UART. IOW, there could be hardware
> translation table access. So we need to ensure the 'dsb' has completed
> before continuing. Therefore add an 'isb'.
>
> Fixes: e79999e587d7 ("xen/arm32: head: Remove 1:1 mapping as soon as it is
> not used")
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
Cheers
Bertrand
> ---
> xen/arch/arm/arm32/head.S | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index f9f7be9588b1..6ca3329138e3 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -751,6 +751,11 @@ setup_fixmap:
> create_table_entry boot_second, xen_fixmap, r0, 2
> /* Ensure any page table updates made above have occurred. */
> dsb nshst
> + /*
> + * The fixmap area will be used soon after. So ensure no hardware
> + * translation happens before the dsb completes.
> + */
> + isb
>
> mov pc, lr
> ENDPROC(setup_fixmap)
> --
> 2.40.1
>
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