About pmap_mapdev() & pmap_unmapdev()

Kohji Okuno
Sat, 04 Oct 2014 08:53:26 -0000

Hi, Konstantin,

> At the end of the mail is commit candidate.  I did not even compiled this.
> Can you test and report back, please ?

Could you check the following?
(1) should use kernel_pmap->pm_stats.resident_count
                          ^^^
    I'm sorry. My patch was wrong.

(2) should use pmap_resident_count_inc() in amd64.


I will test, later.

In addtion, I have one question.
In current and 10-stable, is vm_map_delete() called by kva_free()?
If vm_map_delete() is called, this fix is needed in current and
10-stable, I think.

Regards,
 Kohji Okuno

> On Sat, Oct 04, 2014 at 05:00:36PM +0900, Kohji Okuno wrote:
>> Hi, Konstantin,
>>
>> Thank you for your comment.
>> And, your change is better than mine.
> At the end of the mail is commit candidate.  I did not even compiled this.
> Can you test and report back, please ?
>
>>
>> > Do you mean that this panic is related to missed pmap_remove() ?
>> > I doubt it, since pmap_mapdev() does not establish managed
mappings.
>>
>> Yes, pmap_mapdev() does not establish managed mappings. But, if
>> kernel_pmap.pm_stats.resident_count is zero, then any managed pages
>> (for example pipe_map, exec_map, or etc.) are not able to change
>> unmanaged status, because pmap_remove() returns without calling
>> pmap_remove_pte().
>>
>> In this result, I encounterd the panic. Could you refer the following?
> Yes, kmem_back() indeed uses managed mapping.
>
> Index: amd64/amd64/pmap.c
> ==================================================================> ---
amd64/amd64/pmap.c	(revision 272506)
> +++ amd64/amd64/pmap.c	(working copy)
> @@ -5040,6 +5040,9 @@ pmap_mapdev_attr(vm_paddr_t pa, vm_size_t size, in
>  	pa = trunc_page(pa);
>  	for (tmpsize = 0; tmpsize < size; tmpsize += PAGE_SIZE)
>  		pmap_kenter_attr(va + tmpsize, pa + tmpsize, mode);
> +	PMAP_LOCK(kernel_pmap);
> +	kernel_pmap.pm_stats.resident_count += OFF_TO_IDX(size);
> +	PMAP_UNLOCK(kernel_pmap);
>  	pmap_invalidate_range(kernel_pmap, va, va + tmpsize);
>  	pmap_invalidate_cache_range(va, va + tmpsize);
>  	return ((void *)(va + offset));
> Index: i386/i386/pmap.c
> ==================================================================> ---
i386/i386/pmap.c	(revision 272506)
> +++ i386/i386/pmap.c	(working copy)
> @@ -5066,10 +5066,14 @@ pmap_mapdev_attr(vm_paddr_t pa, vm_size_t size, in
>  	size = roundup(offset + size, PAGE_SIZE);
>  	pa = pa & PG_FRAME;
>
> -	if (pa < KERNLOAD && pa + size <= KERNLOAD)
> +	if (pa < KERNLOAD && pa + size <= KERNLOAD) {
>  		va = KERNBASE + pa;
> -	else
> +	} else {
>  		va = kmem_alloc_nofault(kernel_map, size);
> +		PMAP_LOCK(kernel_pmap);
> +		kernel_pmap.pm_stats.resident_count += OFF_TO_IDX(size);
> +		PMAP_UNLOCK(kernel_pmap);
> +	}
>  	if (!va)
>  		panic("pmap_mapdev: Couldn't alloc kernel virtual
memory");
>
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