Jan Kiszka via Xenomai <xenomai@xenomai.org> writes:
> On 23.05.22 16:04, Gunter Grau via Xenomai wrote:
>> From: Gunter Grau <gunter.g...@philips.com>
>>
>> When mapping io memory into userspace an extra simulated pagefault for all
>> pages is added to prevent later pagefaults because of copy on write
>> mechanisms. This happens only on architectures that have defined the
>> needed cobalt_machine.prefault function.
>>
>> Signed-off-by: Gunter Grau <gunter.g...@philips.com>
>> ---
>> kernel/cobalt/rtdm/drvlib.c | 10 +++++++++-
>> 1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/cobalt/rtdm/drvlib.c b/kernel/cobalt/rtdm/drvlib.c
>> index 4eaf3a57c..db8431ee1 100644
>> --- a/kernel/cobalt/rtdm/drvlib.c
>> +++ b/kernel/cobalt/rtdm/drvlib.c
>> @@ -1761,6 +1761,7 @@ static int mmap_iomem_helper(struct vm_area_struct
>> *vma, phys_addr_t pa)
>> {
>> pgprot_t prot = PAGE_SHARED;
>> unsigned long len;
>> + int ret;
>>
>> len = vma->vm_end - vma->vm_start;
>> #ifndef CONFIG_MMU
>> @@ -1774,8 +1775,15 @@ static int mmap_iomem_helper(struct vm_area_struct
>> *vma, phys_addr_t pa)
>> #endif
>> vma->vm_page_prot = pgprot_noncached(prot);
>>
>> - return remap_pfn_range(vma, vma->vm_start, pa >> PAGE_SHIFT,
>> + ret = remap_pfn_range(vma, vma->vm_start, pa >> PAGE_SHIFT,
>> len, vma->vm_page_prot);
>> + if (ret)
>> + return ret;
>> +
>> + if (cobalt_machine.prefault)
>> + cobalt_machine.prefault(vma);
>> +
>> + return ret;
>> }
>>
>> static int mmap_buffer_helper(struct rtdm_fd *fd, struct vm_area_struct
>> *vma)
>
> Wow, that was likely broken by the refactoring in c8e9e166, long ago.
>
> Applied to next
>
The prefault hook has always been specifically about COW-breaking, I/O
memory has no business with this, so there is no point in having the
iomem helper calling the prefaulting hook.
I suspect that rtdm_mmap_to_user() should be called instead of
rtdm_iomap_to_user() in the case at hand.
--
Philippe.
