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Re: [Qemu-devel] [PATCH v6 01/17] pci: fix unaligned access in pci_xxx_q


From: Dmitry Fleytman
Subject: Re: [Qemu-devel] [PATCH v6 01/17] pci: fix unaligned access in pci_xxx_quad()
Date: Mon, 30 May 2016 18:05:57 +0300

> On 30 May 2016, at 17:47 PM, Michael S. Tsirkin <address@hidden> wrote:
> 
> On Mon, May 30, 2016 at 12:14:26PM +0300, Leonid Bloch wrote:
>> From: Dmitry Fleytman <address@hidden>
>> 
>> Replace legacy cpu_to_le64w()/le64_to_cpup()
>> calls with stq_le_p()/ldq_le_p().
>> 
>> Signed-off-by: Dmitry Fleytman <address@hidden>
>> Signed-off-by: Leonid Bloch <address@hidden>
> 

Hi Michael,

> Could you please add a code comment to clarify what's going on a bit more?
> Something to the point that capabilities are guaranteed to
> be dword-aligned only.
> 

Just to clarify, do you want to add these comments to 
pci_set/get_quad functions or to the new DSN-generation function?

> Also, this isn't a dependency of this patchset I think -
> as far as I could say the only user of this is
>       pcie: Introduce function for DSN capability creation
> but that merely accesses a capability, and all callers pass in
> an aligned offset.

Right, this issue appeared after introduction of DSN generation function.
All other callers pass aligned offsets so far.

Thanks,
Dmitry

> 
>> ---
>> include/hw/pci/pci.h | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
>> index ef6ba51..ee238ad 100644
>> --- a/include/hw/pci/pci.h
>> +++ b/include/hw/pci/pci.h
>> @@ -468,13 +468,13 @@ pci_get_long(const uint8_t *config)
>> static inline void
>> pci_set_quad(uint8_t *config, uint64_t val)
>> {
>> -    cpu_to_le64w((uint64_t *)config, val);
>> +    stq_le_p(config, val);
>> }
>> 
>> static inline uint64_t
>> pci_get_quad(const uint8_t *config)
>> {
>> -    return le64_to_cpup((const uint64_t *)config);
>> +    return ldq_le_p(config);
>> }
>> 
>> static inline void
>> -- 
>> 2.5.5




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