Re: [RFC PATCH-for-9.0 v2 13/19] hw/xen: Remove use of 'target_ulong' in handle_ioreq()

[Anthony PERARD <anthony.perard@cloud.com>]

On Tue, Nov 14, 2023 at 03:38:09PM +0100, Philippe Mathieu-Daudé wrote:
> Per commit f17068c1c7 ("xen-hvm: reorganize xen-hvm and move common
> function to xen-hvm-common"), handle_ioreq() is expected to be
> target-agnostic. However it uses 'target_ulong', which is a target
> specific definition.
> 
> Per xen/include/public/hvm/ioreq.h header:
> 
>   struct ioreq {
>     uint64_t addr;          /* physical address */
>     uint64_t data;          /* data (or paddr of data) */
>     uint32_t count;         /* for rep prefixes */
>     uint32_t size;          /* size in bytes */
>     uint32_t vp_eport;      /* evtchn for notifications to/from device model */
>     uint16_t _pad0;
>     uint8_t state:4;
>     uint8_t data_is_ptr:1;  /* if 1, data above is the guest paddr
>                              * of the real data to use. */
>     uint8_t dir:1;          /* 1=read, 0=write */
>     uint8_t df:1;
>     uint8_t _pad1:1;
>     uint8_t type;           /* I/O type */
>   };
>   typedef struct ioreq ioreq_t;
> 
> If 'data' is not a pointer, it is a u64.
> 
> - In PIO / VMWARE_PORT modes, only 32-bit are used.
> 
> - In MMIO COPY mode, memory is accessed by chunks of 64-bit

Looks like it could also be 8, 16, or 32 as well, depending on
req->size.

> - In PCI_CONFIG mode, access is u8 or u16 or u32.
> 
> - None of TIMEOFFSET / INVALIDATE use 'req'.
> 
> - Fallback is only used in x86 for VMWARE_PORT.
> 
> Masking the upper bits of 'data' to keep 'req->size' low bits
> is irrelevant of the target word size. Remove the word size
> check and always extract the relevant bits.

When building QEMU for Xen, we tend to build the target "i386-softmmu",
which looks like to have target_ulong == uint32_t. So the `data`
clamping would only apply to size 8 and 16. The clamping with
target_ulong was introduce long time ago, here:
https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=b4a663b87df3954557434a2d31bff7f6b2706ec1
and they were more IOREQ types.
So my guess is it isn't relevant anymore, but extending the clamping to
32-bits request should be fine, when using qemu-system-i386 that is, as
it is already be done if one use qemu-system-x86_64.

So I think the patch is fine, and the tests I've ran so far worked fine.

> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

Thanks,

-- 
Anthony PERARD