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Re: [PATCH 1/5] hw/arm/smmuv3: Apply address mask to linear strtab base

From: Auger Eric
Subject: Re: [PATCH 1/5] hw/arm/smmuv3: Apply address mask to linear strtab base address
Date: Mon, 9 Dec 2019 10:14:06 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0

Hi Simon,

On 12/5/19 11:04 PM, Simon Veith wrote:
> Hello Eric,
> On 05/12/2019 09:42, Auger Eric wrote:
>> Not related to this patch but I noticed SMMU_BASE_ADDR_MASK should be
>> 0xffffffffffc0 and not 0xffffffffffe0. I can fix it separately or if you
>> respin, you may fix it as well?
> Good catch, thank you. I'll fix it in the next version.
> Looking at the upper end of that mask, it seems that we are currently masking 
> out bits 48 through 63, rather than just 51 through 63.
> The reference manual says that this should be done to match the system 
> physical address size as given by SMMU_IDR5.OAS.
Yes you're right. This should go up to 51 as per the field range
definition. Spec says address bits and above this field range are
treated as zero.
> We define SMMU_IDR5_OAS to be 4, which selects a physical address size of 44 
> bits (ref. section 6.3.6). I think the mask should therefore be 0xfffffffffc0 
> to clear bits 44 and above. Do you agree?
bits beyond the OAS are RES0. The spec does not says those fields are
treated as zero, as explicitly mentioned for bits > 51. Normally the
guest should not set them to something != 0, this would be a programming
error right? Guest is supposed to read the IDR5 and program accordingly?

> Ideally, we would derive this mask from our definition of SMMU_IDR5_OAS, but 
> I'm not sure it's okay to stuff a call to oas2bits() into the 
Well I am not sure this is worth the candle. I am not sure we are
obliged to enforce this.


> Regards
> Simon
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