From: Peter Xu <peterx@redhat.com>
To: Axel Rasmussen <axelrasmussen@google.com>
Cc: "Alexander Viro" <viro@zeniv.linux.org.uk>,
"Alexey Dobriyan" <adobriyan@gmail.com>,
"Andrea Arcangeli" <aarcange@redhat.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Anshuman Khandual" <anshuman.khandual@arm.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Chinwen Chang" <chinwen.chang@mediatek.com>,
"Huang Ying" <ying.huang@intel.com>,
"Ingo Molnar" <mingo@redhat.com>, "Jann Horn" <jannh@google.com>,
"Jerome Glisse" <jglisse@redhat.com>,
"Lokesh Gidra" <lokeshgidra@google.com>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Michal Koutný" <mkoutny@suse.com>,
"Michel Lespinasse" <walken@google.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Mike Rapoport" <rppt@linux.vnet.ibm.com>,
"Nicholas Piggin" <npiggin@gmail.com>, "Shaohua Li" <shli@fb.com>,
"Shawn Anastasio" <shawn@anastas.io>,
"Steven Rostedt" <rostedt@goodmis.org>,
"Steven Price" <steven.price@arm.com>,
"Vlastimil Babka" <vbabka@suse.cz>,
LKML <linux-kernel@vger.kernel.org>,
linux-fsdevel@vger.kernel.org, "Linux MM" <linux-mm@kvack.org>,
"Adam Ruprecht" <ruprecht@google.com>,
"Cannon Matthews" <cannonmatthews@google.com>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
"David Rientjes" <rientjes@google.com>,
"Oliver Upton" <oupton@google.com>
Subject: Re: [PATCH v3 7/9] userfaultfd: add UFFDIO_CONTINUE ioctl
Date: Mon, 1 Feb 2021 17:40:34 -0500 [thread overview]
Message-ID: <20210201224034.GK260413@xz-x1> (raw)
In-Reply-To: <CAJHvVciv0-Xq75TKB=g=Sb+HmwMdJEd+CHg885TWX2svYCwFiQ@mail.gmail.com>
On Mon, Feb 01, 2021 at 02:11:55PM -0800, Axel Rasmussen wrote:
> On Mon, Feb 1, 2021 at 11:21 AM Peter Xu <peterx@redhat.com> wrote:
> >
> > On Thu, Jan 28, 2021 at 02:48:17PM -0800, Axel Rasmussen wrote:
> > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > > index f94a35296618..79e1f0155afa 100644
> > > --- a/include/linux/hugetlb.h
> > > +++ b/include/linux/hugetlb.h
> > > @@ -135,11 +135,14 @@ void hugetlb_show_meminfo(void);
> > > unsigned long hugetlb_total_pages(void);
> > > vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> > > unsigned long address, unsigned int flags);
> > > +#ifdef CONFIG_USERFAULTFD
> >
> > I'm confused why this is needed.. hugetlb_mcopy_atomic_pte() should only be
> > called in userfaultfd.c, but if without uffd config set it won't compile
> > either:
> >
> > obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
>
> With this series as-is, but *without* the #ifdef CONFIG_USERFAULTFD
> here, we introduce a bunch of build warnings like this:
>
>
>
> In file included from ./include/linux/migrate.h:8:0,
> from kernel/sched/sched.h:53,
> from kernel/sched/isolation.c:10:
> ./include/linux/hugetlb.h:143:12: warning: 'enum mcopy_atomic_mode'
> declared inside parameter list
> struct page **pagep);
> ^
> ./include/linux/hugetlb.h:143:12: warning: its scope is only this
> definition or declaration, which is probably not what you want
>
> And similarly we get an error about the "mode" parameter having an
> incomplete type in hugetlb.c.
>
>
>
> This is because enum mcopy_atomic_mode is defined in userfaultfd_k.h,
> and that entire header is wrapped in a #ifdef CONFIG_USERFAULTFD. So
> we either need to define enum mcopy_atomic_mode unconditionally, or we
> need to #ifdef CONFIG_USERFAULTFD the references to it also.
>
> - I opted not to move it outside the #ifdef CONFIG_USERFAULTFD in
> userfaultfd_k.h (defining it unconditionally), because that seemed
> messy to me.
> - I opted not to define it unconditionally in hugetlb.h, because we'd
> have to move it to userfaultfd_k.h anyway when shmem or other users
> are introduced. I'm planning to send a series to add this a few days
> or so after this series is merged, so it seems churn-y to move it
> then.
> - It seemed optimal to not compile hugetlb_mcopy_atomic_pte anyway
> (even ignoring adding the continue ioctl), since as you point out
> userfaultfd is the only caller.
>
> Hopefully this clarifies this and the next two comments. Let me know
> if you still feel strongly, I don't hate any of the alternatives, just
> wanted to clarify that I had considered them and thought this approach
> was best.
Then I'd suggest you use a standalone patch to put hugetlb_mcopy_atomic_pte()
into CONFIG_USERFAULTFD blocks, then propose your change with the minor mode.
Note that there're two hugetlb_mcopy_atomic_pte() defined in hugetlb.h.
Although I don't think it a problem since the other one is inlined - I think
you should still put that one into the same ifdef:
#ifdef CONFIG_USERFAULTFD
static inline int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
pte_t *dst_pte,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr,
struct page **pagep)
{
BUG();
return 0;
}
#endif /* CONFIG_USERFAULTFD */
Let's also see whether Mike would have a preference on this.
Thanks,
--
Peter Xu
next prev parent reply other threads:[~2021-02-01 22:40 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-28 22:48 [PATCH v3 0/9] userfaultfd: add minor fault handling Axel Rasmussen
2021-01-28 22:48 ` [PATCH v3 1/9] hugetlb: Pass vma into huge_pte_alloc() Axel Rasmussen
2021-01-28 23:42 ` [PATCH v4 " Axel Rasmussen
2021-02-01 21:38 ` Mike Kravetz
2021-02-01 21:53 ` Mike Kravetz
2021-02-01 22:16 ` Peter Xu
2021-01-28 22:48 ` [PATCH v3 2/9] hugetlb/userfaultfd: Forbid huge pmd sharing when uffd enabled Axel Rasmussen
2021-02-01 22:01 ` Mike Kravetz
2021-01-28 22:48 ` [PATCH v3 3/9] mm/hugetlb: Move flush_hugetlb_tlb_range() into hugetlb.h Axel Rasmussen
2021-02-01 22:09 ` Mike Kravetz
2021-01-28 22:48 ` [PATCH v3 4/9] hugetlb/userfaultfd: Unshare all pmds for hugetlbfs when register wp Axel Rasmussen
2021-02-01 22:33 ` Mike Kravetz
2021-02-01 23:21 ` Peter Xu
2021-01-28 22:48 ` [PATCH v3 5/9] userfaultfd: add minor fault registration mode Axel Rasmussen
2021-02-01 18:31 ` Peter Xu
2021-02-02 17:15 ` Peter Xu
2021-02-03 18:20 ` Axel Rasmussen
2021-01-28 22:48 ` [PATCH v3 6/9] userfaultfd: disable huge PMD sharing for MINOR registered VMAs Axel Rasmussen
2021-01-28 22:48 ` [PATCH v3 7/9] userfaultfd: add UFFDIO_CONTINUE ioctl Axel Rasmussen
2021-02-01 19:21 ` Peter Xu
2021-02-01 22:11 ` Axel Rasmussen
2021-02-01 22:40 ` Peter Xu [this message]
2021-02-01 23:42 ` Mike Kravetz
2021-02-01 22:41 ` Lokesh Gidra
2021-01-28 22:48 ` [PATCH v3 8/9] userfaultfd: update documentation to describe minor fault handling Axel Rasmussen
2021-02-01 20:06 ` Peter Xu
2021-02-02 23:07 ` Axel Rasmussen
2021-01-28 22:48 ` [PATCH v3 9/9] userfaultfd/selftests: add test exercising " Axel Rasmussen
2021-02-01 19:33 ` Peter Xu
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