Re: [PATCH v2 02/17] system/memory: Better describe @plen argument of flatview_translate()

[Thomas Huth <thuth@redhat.com>]

On 30/09/2025 06.13, Philippe Mathieu-Daudé wrote:
> flatview_translate()'s @plen argument is output-only and can be NULL.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>   include/system/memory.h | 5 +++--
>   system/physmem.c        | 6 +++---
>   2 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/include/system/memory.h b/include/system/memory.h
> index aa85fc27a10..3e5bf3ef05e 100644
> --- a/include/system/memory.h
> +++ b/include/system/memory.h
> @@ -2992,13 +2992,14 @@ IOMMUTLBEntry address_space_get_iotlb_entry(AddressSpace *as, hwaddr addr,
>    * @addr: address within that address space
>    * @xlat: pointer to address within the returned memory region section's
>    * #MemoryRegion.
> - * @len: pointer to length
> + * @plen_out: pointer to valid read/write length of the translated address.
> + *            It can be @NULL when we don't care about it.
>    * @is_write: indicates the transfer direction
>    * @attrs: memory attributes
>    */
>   MemoryRegion *flatview_translate(FlatView *fv,
>                                    hwaddr addr, hwaddr *xlat,
> -                                 hwaddr *len, bool is_write,
> +                                 hwaddr *plen_out, bool is_write,
>                                    MemTxAttrs attrs);
>   
>   static inline MemoryRegion *address_space_translate(AddressSpace *as,
> diff --git a/system/physmem.c b/system/physmem.c
> index 8a8be3a80e2..2d1697fce4c 100644
> --- a/system/physmem.c
> +++ b/system/physmem.c
> @@ -566,7 +566,7 @@ iotlb_fail:
>   
>   /* Called from RCU critical section */
>   MemoryRegion *flatview_translate(FlatView *fv, hwaddr addr, hwaddr *xlat,
> -                                 hwaddr *plen, bool is_write,
> +                                 hwaddr *plen_out, bool is_write,
>                                    MemTxAttrs attrs)
>   {
>       MemoryRegion *mr;
> @@ -574,13 +574,13 @@ MemoryRegion *flatview_translate(FlatView *fv, hwaddr addr, hwaddr *xlat,
>       AddressSpace *as = NULL;
>   
>       /* This can be MMIO, so setup MMIO bit. */
> -    section = flatview_do_translate(fv, addr, xlat, plen, NULL,
> +    section = flatview_do_translate(fv, addr, xlat, plen_out, NULL,
>                                       is_write, true, &as, attrs);
>       mr = section.mr;
>   
>       if (xen_enabled() && memory_access_is_direct(mr, is_write, attrs)) {
>           hwaddr page = ((addr & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE) - addr;
> -        *plen = MIN(page, *plen);
> +        *plen_out = MIN(page, *plen_out);

There is no check for a NULL pointer here, so plen_out must *not* be NULL?
Or did I miss something?

  Thomas


>       }
>   
>       return mr;