linux-kernel - Re: [RFC PATCH v3 1/6] arch: introduce set_direct_map_valid

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Message-ID: <a774e13e-0616-4d96-bb51-bac0fcb2cb9b@redhat.com>
Date: Thu, 31 Oct 2024 10:57:21 +0100
From: David Hildenbrand <david@...hat.com>
To: Patrick Roy <roypat@...zon.co.uk>, tabba@...gle.com,
 quic_eberman@...cinc.com, seanjc@...gle.com, pbonzini@...hat.com,
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Subject: Re: [RFC PATCH v3 1/6] arch: introduce set_direct_map_valid_noflush()

On 30.10.24 14:49, Patrick Roy wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
> 
> From: Mike Rapoport (Microsoft) <rppt@...nel.org>
> 
> Add an API that will allow updates of the direct/linear map for a set of
> physically contiguous pages.
> 
> It will be used in the following patches.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> Signed-off-by: Patrick Roy <roypat@...zon.co.uk>


[...]

>   #ifdef CONFIG_DEBUG_PAGEALLOC
>   void __kernel_map_pages(struct page *page, int numpages, int enable)
>   {
> diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h
> index e7aec20fb44f1..3030d9245f5ac 100644
> --- a/include/linux/set_memory.h
> +++ b/include/linux/set_memory.h
> @@ -34,6 +34,12 @@ static inline int set_direct_map_default_noflush(struct page *page)
>   	return 0;
>   }
>   
> +static inline int set_direct_map_valid_noflush(struct page *page,
> +					       unsigned nr, bool valid)

I recall that "unsigned" is frowned upon; "unsigned int".

> +{
> +	return 0;
> +}

Can we add some kernel doc for this?

In particular

(a) What does it mean when we return 0? That it worked? Then, this
     dummy function looks wrong. Or this it return the
     number of processed entries? Then we'd have a possible "int" vs.
     "unsigned int" inconsistency.

(b) What are the semantics when we fail halfway through the operation
     when processing nr > 1? Is it "all or nothing"?


-- 
Cheers,

David / dhildenb