Am 2022-02-17 um 19:19 schrieb Jason Gunthorpe:
On Thu, Feb 17, 2022 at 04:12:20PM -0500, Felix Kuehling wrote:
I'm thinking of a more theoretical approach: Instead of auditing all users,
I'd ask, what are the invariants that a vm_normal_page should have. Then
check, whether our DEVICE_COHERENT pages satisfy them. But maybe the concept
of a vm_normal_page isn't defined clearly enough for that.
I would say the expectation is that only 'page cache and anon' pages
are returned - ie the first union in struct page
This is because the first file in your list I looked at:
static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
page = vm_normal_page(vma, addr, ptent);
[..]
if (pageout) {
if (!isolate_lru_page(page)) {
Uses the LRU field, so this is incompatible with all the other page
types.
One mitigation of this might be to formally make vm_normal_page() ==
'pte to page cache and anon page' and add a new function that is 'pte
to any struct page'
Then go through and sort callers as appropriate.
The 'pte to page cache and anon page' can detect ZONE_DEVICE by
calling is_zone_device_page() insted of pte_devmap() and then continue
to return NULL. This same trick will fix GUP_fast.
Sounds good to me. What about vm_normal_page_pmd? Should we remove the
pmd_devmap check from that function as well. I'm not even sure what a
huge zone_device page would look like, but maybe that's a worthwhile
future optimization for our driver.
I'd propose the function names vm_normal_page and
vm_normal_or_device_page for the two functions you described. The latter
would basically be the current vm_normal_page with the pte_devmap check
removed. vm_normal_page could be implemented as a wrapper around
vm_normal_or_device_page, which just adds the !is_zone_device_page() check.
Regards,
Felix
Jason
