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Re: [PATCH v1 2/3] xen/riscv: update defintion of vmap_to_mfn()
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 27 Jan 2025 11:09:05 +0100
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- Cc: Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 27 Jan 2025 10:09:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.01.2025 17:54, Oleksii Kurochko wrote:
> vmap_to_mfn() uses virt_to_maddr(), which is designed to work with VA from
> either the direct map region or Xen's linkage region (XEN_VIRT_START).
> An assertion will occur if it is used with other regions, in particular for
> the VMAP region.
>
> Since RISC-V lacks a hardware feature to request the MMU to translate a VA to
> a PA (as Arm does, for example), software page table walking (pt_walk()) is
> used for the VMAP region to obtain the PA.
>
> Fixes: 7db8d2bd9b ("xen/riscv: add minimal stuff to mm.h to build full Xen")
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> --- a/xen/arch/riscv/include/asm/mm.h
> +++ b/xen/arch/riscv/include/asm/mm.h
> @@ -25,7 +25,7 @@ paddr_t pt_walk(vaddr_t va);
> #define gaddr_to_gfn(ga) _gfn(paddr_to_pfn(ga))
> #define mfn_to_maddr(mfn) pfn_to_paddr(mfn_x(mfn))
> #define maddr_to_mfn(ma) _mfn(paddr_to_pfn(ma))
> -#define vmap_to_mfn(va) maddr_to_mfn(virt_to_maddr((vaddr_t)(va)))
> +#define vmap_to_mfn(va) maddr_to_mfn(pt_walk((vaddr_t)(va)))
With this being the first use of pt_walk(), I wonder whether the function might
better return mfn_t (and simply ignore the low 12 bits of Vthe incoming VA; see
my respective comment on the earlier patch). After all it is quite natural for
a page table walk to return a page frame number, not a physical address.
Jan
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