linux-kernel - Re: [Xen-devel] [PATCH 1/4] xen: re-introduce support for grant v2 interface

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Message-ID: <67503f2a-6d93-59c6-5a49-40fcb487859c@oracle.com>
Date:   Tue, 12 Sep 2017 11:41:19 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [Xen-devel] [PATCH 1/4] xen: re-introduce support for grant v2
 interface


> +int arch_gnttab_map_status(uint64_t *frames, unsigned long nr_gframes,
> +			   unsigned long max_nr_gframes,
> +			   grant_status_t **__shared)
> +{
> +	grant_status_t *shared = *__shared;
> +	unsigned long addr;
> +	unsigned long i;
> +
> +	if (shared == NULL)
> +		*__shared = shared = gnttab_status_vm_area.area->addr;
> +
> +	addr = (unsigned long)shared;
> +
> +	for (i = 0; i < nr_gframes; i++) {
> +		set_pte_at(&init_mm, addr, gnttab_status_vm_area.ptes[i],
> +			   mfn_pte(frames[i], PAGE_KERNEL));
> +		addr += PAGE_SIZE;
> +	}
> +
> +	return 0;
> +}

This looks pretty much identical to arch_gnttab_map_shared() except for
gnttab_shared_vm_area vs. gnttab_status_vm_area,which can be passed in
as a parameter.

> +
>  void arch_gnttab_unmap(void *shared, unsigned long nr_gframes)
>  {
> +	pte_t **ptes;
>  	unsigned long addr;
>  	unsigned long i;
>  
> +	if (shared == gnttab_status_vm_area.area->addr)
> +		ptes = gnttab_status_vm_area.ptes;
> +	else
> +		ptes = gnttab_shared_vm_area.ptes;
> +
>  	addr = (unsigned long)shared;
>  
>  	for (i = 0; i < nr_gframes; i++) {
> -		set_pte_at(&init_mm, addr, gnttab_shared_vm_area.ptes[i],
> -			   __pte(0));
> +		set_pte_at(&init_mm, addr, ptes[i], __pte(0));
>  		addr += PAGE_SIZE;
>  	}

And this too looks like can be factored out (to something like
arch_update_gnttab()). But perhaps not in this patch.

>  }
> @@ -102,12 +129,35 @@ static int arch_gnttab_valloc(struct gnttab_vm_area *area, unsigned nr_frames)
>  	return 0;
>  }
>  
> -int arch_gnttab_init(unsigned long nr_shared)
> +static void arch_gnttab_vfree(struct gnttab_vm_area *area)
>  {
> +	free_vm_area(area->area);
> +	kfree(area->ptes);
> +}

Not sure there is need for this routine. It is used only once.

Also, as an overall comment -- It feels like there may be too many
BUG_ON()s.


-boris