Re: [PATCH] arm/ioreq: clean data field in ioreq struct on read operations

[Julien Grall <julien@xxxxxxx>]

On 04/10/2023 09:42, Andrii Chepurnyi wrote:
> Hello,
Hi,

> On 10/3/23 16:49, Julien Grall wrote:
> > Hi,
> >
> > On 03/10/2023 14:19, Andrii Chepurnyi wrote:
> > > For read operations, there's a potential issue when the data field
> > > of the ioreq struct is partially updated in the response. To address
> > > this, zero data field during read operations. This modification
> > > serves as a safeguard against implementations that may inadvertently
> > > partially update the data field in response to read requests.
> > > For instance, consider an 8-bit read operation. In such cases, QEMU,
> > > returns the same content of the data field with only 8 bits of
> > > updated data.
> > Do you have a pointer to the code?
> First of all, using the term "user-space" with respect to this problem
> was a mistake from my side.
>
> In general, my use case is to run u-boot with virtio-blk inside the
> guest domain.
> I.e. setup configuration(hardware renesas gen3 kingfisher board):  Dom0,
> DomD ( QEMU as backend) and running u-boot in DomA with virtio-blk.
> The problem appeared inside the u-boot code :
I was asking a pointer to the code in the Device Emulator (QEMU in your 
case). I am confident the code is correct in U-boot, because when using 
'w0', the unused bits are meant to be set to zero (per the Arm Arm). But 
I am curious to know why QEMU is not doing it.
Cheers,

--
Julien Grall