Re: [Qemu-devel] [Qemu-ppc] [PATCH] spapr_iommu: fix erroneous sanity check in h_put_tce_indirect()

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 06/16/2015 07:24 PM, Greg Kurz wrote:
> On Tue, 16 Jun 2015 18:53:51 +1000
> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
>
>> On 06/16/2015 03:28 AM, Greg Kurz wrote:
>>> According to PAPR+ 3.2.2.2, the TCE is implemented as follows:
>>> 	bits  0-51: real page number
>>> 	bits 52-61: reserved for future use
>>> 	bits 62-63: page protection (read-only, write-only, read-write)
>>
>>
>>
>> tce_list is not a TCE, it is "The logical address of a page of (4 K long on
>> a 4 K boundary) of TCE contents to be stored in the TCE table (contains
>> logical address of storage page to be mapped)" so we rather want to remove
>> (tce_list & ~SPAPR_TCE_RW) below.
>>
>
> Oops my bad for the confustion... :-\
>
> Then it looks like SPAPR_TCE_RW can be dropped as well since put_tce_emu() uses
> IOMMU_RW instead.


Well, spapr_tce_translate_iommu() should actually translate SPAPR_TCE_xxx 
(PAPR defined flags) to IOMMU_xxx (QEMU IOMMUTLBEntry permission bits), not 
just rely on the fact that they match.


>
>>
>>> Possible values for the protection bits are necessarly non-zero and thus
>>> H_PUT_TCE_INDIRECT currently always fails and returns H_PARAMETER.
>>>
>>> The code explicitly clears the protection bits when computing the TCE offset,
>>> a few lines below (tce_list & ~SPAPR_TCE_RW)... The sanity check is obviously
>>> wrong for these bits.
>>>
>>> Moreover, I could find no indication in PAPR+ that using the other reserved
>>> bits should error out with H_PARAMETER.
>>>
>>> This patch simply drops the offending check.
>>>
>>> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
>>> ---
>>>    hw/ppc/spapr_iommu.c |    2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
>>> index 8cd9dba9ac4d..37a1110c9d87 100644
>>> --- a/hw/ppc/spapr_iommu.c
>>> +++ b/hw/ppc/spapr_iommu.c
>>> @@ -258,7 +258,7 @@ static target_ulong h_put_tce_indirect(PowerPCCPU *cpu,
>>>            return H_PARAMETER;
>>>        }
>>>
>>> -    if ((npages > 512) || (tce_list & SPAPR_TCE_PAGE_MASK)) {
>>> +    if (npages > 512) {
>>>            return H_PARAMETER;
>>>        }
>>>
>>>
>>>
>>
>>
>


-- 
Alexey