Re: [RFC PATCH v2 1/3] mm/gup: fix gup_fast with dynamic page table folding
From: Jason Gunthorpe <jgg@ziepe.ca>
Date: 2020-09-10 23:21:21
Also in:
linux-arch, linux-mm, linux-s390, linux-um, linuxppc-dev, lkml, sparclinux
On Thu, Sep 10, 2020 at 07:57:49PM +0200, Gerald Schaefer wrote:
On Thu, 10 Sep 2020 10:02:33 -0300 Jason Gunthorpe [off-list ref] wrote:quoted
On Thu, Sep 10, 2020 at 11:39:25AM +0200, Alexander Gordeev wrote:quoted
As Gerald mentioned, it is very difficult to explain in a clear way. Hopefully, one could make sense ot of it.I would say the page table API requires this invariant: pud = pud_offset(p4d, addr); do { WARN_ON(pud != pud_offset(p4d, addr); next = pud_addr_end(addr, end); } while (pud++, addr = next, addr != end); ie pud++ is supposed to be a shortcut for pud_offset(p4d, next)Hmm, IIUC, all architectures with static folding will simply return the passed-in p4d pointer for pud_offset(p4d, addr), for 3-level pagetables.
It is probably moot now, but since other arch's don't crash they also return pud_addr_end() == end so the loop only does one iteration. ie pud == pud_offset(p4d, addr) for all iterations as the pud++ never happens. Which is what this addr_end patch does for s390.. Jason _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel