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Re: [PATCH v2 for 4.20? 1/3] xen/riscv: implement software page table walking


  • To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 6 Feb 2025 12:15:08 +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: Thu, 06 Feb 2025 11:15:14 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 05.02.2025 17:55, Oleksii Kurochko wrote:
> On 2/4/25 2:50 PM, Jan Beulich wrote:
>> On 03.02.2025 14:12, Oleksii Kurochko wrote:
>>> --- a/xen/arch/riscv/include/asm/mm.h
>>> +++ b/xen/arch/riscv/include/asm/mm.h
>>> @@ -156,6 +156,10 @@ static inline struct page_info *virt_to_page(const 
>>> void *v)
>>>       return frametable_virt_start + PFN_DOWN(va - directmap_virt_start);
>>>   }
>>>   
>>> +#include <asm/page.h>
>> asm/page.h already includes asm/mm.h, so you're introducing a circular
>> dependency here (much of which the patch description is about, so it's
>> unclear why you didn't solve this another way). Afaict ...
>>
>>> +pte_t * pt_walk(vaddr_t va, unsigned int *pte_level);
>> ... it's pte_t that presents a problem here. Why not simply put the
>> declaration in asm/page.h (and drop all the secondary changes that
>> don't really belong in this patch anyway)?
> 
> In the patch 2 it is used for implementing vmap_to_mfn():
> 
>    static inline mfn_t vmap_to_mfn_(vaddr_t va)
>    {
>        pte_t *entry = pt_walk(va, NULL);
> 
>        BUG_ON(!pte_is_mapping(*entry));
> 
>        return mfn_from_pte(*entry);
>    }
> 
>    #define vmap_to_mfn(va)     vmap_to_mfn_((vaddr_t)va)mfn_from_pte
> 
> what leads to including of <asm/page.h> in <asm/mm.h>.
> 
> As an option, if to move the following to <asm/page.h>:
>    #define vmap_to_mfn(va)     vmap_to_mfn_((vaddr_t)va)
>    #define vmap_to_page(va)    mfn_to_page(vmap_to_mfn(va))
> the circular dependency could be dropped.

I wouldn't like that, but it's an option, yes. Alternatives I can think of
right away:
- put the helper function an asm/page.h, but keep the macros where they are,
- convert the helper function to a helper macro.

Jan



 


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