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Re: [PATCH v2 03/10] xen/arm: smmuv3: Ensure queue is read after updating prod pointer
- To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Rahul Singh <Rahul.Singh@xxxxxxx>
- Date: Mon, 5 Sep 2022 09:18:43 +0000
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- Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Zhou Wang <wangzhou1@xxxxxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Will Deacon <will@xxxxxxxxxx>
- Delivery-date: Mon, 05 Sep 2022 09:18:57 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH v2 03/10] xen/arm: smmuv3: Ensure queue is read after updating prod pointer
Hi Stefano,
> On 3 Sep 2022, at 12:21 am, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
>
> On Fri, 2 Sep 2022, Rahul Singh wrote:
>> From: Zhou Wang <wangzhou1@xxxxxxxxxxxxx>
>>
>> Backport Linux commit a76a37777f2c. This is the clean backport without
>> any changes.
>>
>> Reading the 'prod' MMIO register in order to determine whether or
>> not there is valid data beyond 'cons' for a given queue does not
>> provide sufficient dependency ordering, as the resulting access is
>> address dependent only on 'cons' and can therefore be speculated
>> ahead of time, potentially allowing stale data to be read by the
>> CPU.
>>
>> Use readl() instead of readl_relaxed() when updating the shadow copy
>> of the 'prod' pointer, so that all speculated memory reads from the
>> corresponding queue can occur only from valid slots.
>>
>> Signed-off-by: Zhou Wang <wangzhou1@xxxxxxxxxxxxx>
>> Link:
>> https://lore.kernel.org/r/1601281922-117296-1-git-send-email-wangzhou1@xxxxxxxxxxxxx
>> [will: Use readl() instead of explicit barrier. Update 'cons' side to match.]
>> Signed-off-by: Will Deacon <will@xxxxxxxxxx>
>> Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>> a76a37777f2c
>> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
>> ---
>> Changes in v2:
>> - fix commit msg
>> - add _iomb changes also from the origin patch
>> ---
>> xen/arch/arm/include/asm/system.h | 1 +
>> xen/drivers/passthrough/arm/smmu-v3.c | 11 +++++++++--
>> 2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/arm/include/asm/system.h
>> b/xen/arch/arm/include/asm/system.h
>> index 65d5c8e423..fe27cf8c5e 100644
>> --- a/xen/arch/arm/include/asm/system.h
>> +++ b/xen/arch/arm/include/asm/system.h
>> @@ -29,6 +29,7 @@
>> #endif
>>
>> #define smp_wmb() dmb(ishst)
>> +#define __iomb() dmb(osh)
>
> We don't have any other #define starting with __ in system.h.
> I wonder if we should call this macro differently or simply iomb().
I think either iomb() or dma_mb() will be the right name.
Please let me know your view on this.
Regards,
Rahul
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