Re: [PATCH v3 18/20] xen/riscv: implement mfn_valid() and page reference, ownership handling helpers

[Jan Beulich <jbeulich@xxxxxxxx>]

On 31.07.2025 17:58, Oleksii Kurochko wrote:
> Implement the mfn_valid() macro to verify whether a given MFN is valid by
> checking that it falls within the range [start_page, max_page).
> These bounds are initialized based on the start and end addresses of RAM.
> 
> As part of this patch, start_page is introduced and initialized with the
> PFN of the first RAM page.
> Also, initialize pdx_group_valid() by calling set_pdx_range() when
> memory banks are being mapped.
> 
> Also, after providing a non-stub implementation of the mfn_valid() macro,
> the following compilation errors started to occur:
>   riscv64-linux-gnu-ld: prelink.o: in function `__next_node':
>   /build/xen/./include/xen/nodemask.h:202: undefined reference to 
> `page_is_ram_type'
>   riscv64-linux-gnu-ld: prelink.o: in function `get_free_buddy':
>   /build/xen/common/page_alloc.c:881: undefined reference to 
> `page_is_ram_type'
>   riscv64-linux-gnu-ld: prelink.o: in function `alloc_heap_pages':
>   /build/xen/common/page_alloc.c:1043: undefined reference to 
> `page_get_owner_and_reference'
>   riscv64-linux-gnu-ld: /build/xen/common/page_alloc.c:1098: undefined 
> reference to `page_is_ram_type'
>   riscv64-linux-gnu-ld: prelink.o: in function `ns16550_interrupt':
>   /build/xen/drivers/char/ns16550.c:205: undefined reference to `get_page'
>   riscv64-linux-gnu-ld: ./.xen-syms.0: hidden symbol 
> `page_get_owner_and_reference' isn't defined
>   riscv64-linux-gnu-ld: final link failed: bad value
>   make[2]: *** [arch/riscv/Makefile:35: xen-syms] Error 1
> To resolve these errors, the following functions have also been introduced,
> based on their Arm counterparts:
> - page_get_owner_and_reference() and its variant to safely acquire a
>   reference to a page and retrieve its owner.
> - A stub for page_is_ram_type() that currently always returns 0 and asserts
>   unreachable, as RAM type checking is not yet implemented.

For this latter part I can only repeat that the code is reachable, and hence it
is wrong to put ASSERT_UNREACHABLE() there. That's true for Arm's code as well.

> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

With said line dropped:
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan