linux-kernel - Re: [PATCH v11 1/1] vfio/nvgpu: Add vfio pci variant module for grace hopper

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Message-ID: <a080c284-e9e3-452a-9ce2-56c93ef04c02@gmail.com>
Date:   Wed, 11 Oct 2023 12:45:55 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     ankita@...dia.com, jgg@...dia.com, yishaih@...dia.com,
        shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
        aniketa@...dia.com, cjia@...dia.com, kwankhede@...dia.com,
        targupta@...dia.com, vsethi@...dia.com, acurrid@...dia.com,
        apopple@...dia.com, jhubbard@...dia.com, danw@...dia.com,
        anuaggarwal@...dia.com, dnigam@...dia.com, udhoke@...dia.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 1/1] vfio/nvgpu: Add vfio pci variant module for grace
 hopper

On 10/10/2023 02:36, Alex Williamson wrote:
> On Sun, 8 Oct 2023 07:06:41 +0700
> Bagas Sanjaya <bagasdotme@...il.com> wrote:
> 
>> On Sun, Oct 08, 2023 at 01:52:54AM +0530, ankita@...dia.com wrote:
>>> PCI BAR are aligned to the power-of-2, but the actual memory on the
>>> device may not. A read or write access to the physical address from the
>>> last device PFN up to the next power-of-2 aligned physical address
>>> results in reading ~0 and dropped writes.
>>>   
>>
>> Reading garbage or padding in that case?
>>
>> Confused...
> 
> The coherent memory size is rounded to a power-of-2 to be compliant with
> PCI BAR semantics, but reading beyond the implemented size fills the
> return buffer with -1 data, as is common on many platforms when reading
> from an unimplemented section of the address space.  Thanks,
> 
> Alex
> 

Thanks for the explanation!

-- 
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