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SubjectRe: [PATCH v2] xen: Convert kmap() to kmap_local_page()
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On mercoledì 20 aprile 2022 08:03:05 CEST Julia Lawall wrote:
>
> On Wed, 20 Apr 2022, Alaa Mohamed wrote:
>
> > kmap() is being deprecated and these usages are all local to the thread
> > so there is no reason kmap_local_page() can't be used.
> >
> > Replace kmap() calls with kmap_local_page().
>
> OK, so from a Coccinelle point of view, could we do
>
> @@
> expression e1,e2,x,f;
> @@
>
> e1 =
> - kmap
> + kmap_local_page
> (e2)
> ... when != x = e1 // not stored in any location and not passed to
another function
> when != f(...,e1,...)
> when != x = e2
> when != f(...,e2,...)
> -kunmap(e2)
> +kunmap_local(e1)
>
> julia
>

I've never spent sufficient time to understand properly the syntax and
semantics of expressions of Coccinelle. However, thanks Julia, this code
looks good and can be very helpful.

Only a minor objection... it doesn't tell when 'e2' has been allocated
within the same function where the kmap() call is.

In the particular case that I cite above, I'd prefer to remove the
allocation of the page (say with alloc_page()) and convert kmap() /kunmap()
to use kmalloc() / kfree().

Fox example, this is done in the following patch:

commit 633b0616cfe0 ("x86/sgx: Remove unnecessary kmap() from
sgx_ioc_enclave_init()") from Ira Weiny.

Can Coccinelle catch also those special cases where a page that is passed
to kmap() is allocated within that same function (vs. being passed as
argument to this function) and, if so, propose a replacement with
kmalloc()?

Thanks,

Fabio



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