Re: [PATCH v2 03/11] xen/riscv: implement copy_to_guest_phys()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.03.2026 17:29, Oleksii Kurochko wrote:
> Introduce copy_to_guest_phys() for RISC-V, based on the Arm implementation.
> 
> Add a generic copy_guest() helper for copying to and from guest physical
> (and potentially virtual addresses in the future), and implement
> translate_get_page() to translate a guest physical address into a struct
> page_info via the domain p2m.
> 
> Compared to the Arm code:
> - Drop COPY_flush_dcache(), as no such use cases exist on RISC-V.
> - Do not implement the linear mapping case, which is currently unused.
> - Use PAGE_OFFSET() to initialize the local offset variable in copy_guest().
> 
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
preferably with ...

> +static unsigned int copy_guest(void *buf, uint64_t addr, unsigned int len,
> +                               copy_info_t info, unsigned int flags)
> +{
> +    unsigned int offset = PAGE_OFFSET(addr);
> +
> +    BUILD_BUG_ON((sizeof(addr)) < sizeof(vaddr_t));
> +    BUILD_BUG_ON((sizeof(addr)) < sizeof(paddr_t));
> +
> +    while ( len )
> +    {
> +        void *p;
> +        unsigned int size = min(len, (unsigned int)PAGE_SIZE - offset);
> +        struct page_info *page;
> +
> +        page = translate_get_page(info, addr, flags & COPY_gva,
> +                                  flags & COPY_to_guest);
> +        if ( page == NULL )

... this consistent ("!page") with ....

> +            return len;
> +
> +        p = __map_domain_page(page);
> +        p += offset;
> +        if ( flags & COPY_to_guest )
> +        {
> +            /*
> +             * buf will be NULL when the caller request to zero the
> +             * guest memory.
> +             */
> +            if ( buf )

... this.

> +                memcpy(p, buf, size);
> +            else
> +                memset(p, 0, size);
> +        }
> +        else
> +            memcpy(buf, p, size);
> +
> +        unmap_domain_page(p - offset);

It doesn't look like the subtracting of "offset" would be needed here. Any
pointer into the correct page will do.

Jan