| Message ID | 20210204171619.3640084-1-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: Export follow_pte() for KVM so that KVM can stop using follow_pfn() | expand |
On 04/02/21 18:16, Sean Christopherson wrote: > Export follow_pte() to fix build breakage when KVM is built as a module. > An in-flight KVM fix switches from follow_pfn() to follow_pte() in order > to grab the page protections along with the PFN. > > Fixes: bd2fae8da794 ("KVM: do not assume PTE is writable after follow_pfn") > Cc: David Stevens <stevensd@google.com> > Cc: Jann Horn <jannh@google.com> > Cc: Jason Gunthorpe <jgg@ziepe.ca> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: kvm@vger.kernel.org > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > > Paolo, maybe you can squash this with the appropriate acks? Indeed, you beat me by a minute. This change is why I hadn't sent out the patch yet. Andrew or Jason, ok to squash this? Paolo > mm/memory.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/memory.c b/mm/memory.c > index feff48e1465a..15cbd10afd59 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4775,6 +4775,7 @@ int follow_pte(struct mm_struct *mm, unsigned long address, > out: > return -EINVAL; > } > +EXPORT_SYMBOL_GPL(follow_pte); > > /** > * follow_pfn - look up PFN at a user virtual address >
On Thu, Feb 04, 2021 at 06:19:13PM +0100, Paolo Bonzini wrote: > On 04/02/21 18:16, Sean Christopherson wrote: > > Export follow_pte() to fix build breakage when KVM is built as a module. > > An in-flight KVM fix switches from follow_pfn() to follow_pte() in order > > to grab the page protections along with the PFN. > > > > Fixes: bd2fae8da794 ("KVM: do not assume PTE is writable after follow_pfn") > > Cc: David Stevens <stevensd@google.com> > > Cc: Jann Horn <jannh@google.com> > > Cc: Jason Gunthorpe <jgg@ziepe.ca> > > Cc: Paolo Bonzini <pbonzini@redhat.com> > > Cc: kvm@vger.kernel.org > > Signed-off-by: Sean Christopherson <seanjc@google.com> > > > > Paolo, maybe you can squash this with the appropriate acks? > > Indeed, you beat me by a minute. This change is why I hadn't sent out the > patch yet. > > Andrew or Jason, ok to squash this? I think usual process would be to put this in the patch/series/pr that needs it. Given how badly follow_pfn has been misused, I would greatly prefer to see you add a kdoc along with exporting it - making it clear about the rules. And it looks like we should remove the range argument for modular use And document the locking requirements, it does a lockless read of the page table: pgd = pgd_offset(mm, address); if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd))) goto out; p4d = p4d_offset(pgd, address); It doesn't do the trickery that fast GUP does, so it must require the mmap sem in read mode at least. Not sure I understand how fsdax is able to call it only under the i_mmap_lock_read lock? What prevents a page table level from being freed concurrently? And it is missing READ_ONCE's for the lockless page table walk.. :( Jason
diff --git a/mm/memory.c b/mm/memory.c index feff48e1465a..15cbd10afd59 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4775,6 +4775,7 @@ int follow_pte(struct mm_struct *mm, unsigned long address, out: return -EINVAL; } +EXPORT_SYMBOL_GPL(follow_pte); /** * follow_pfn - look up PFN at a user virtual address
Export follow_pte() to fix build breakage when KVM is built as a module. An in-flight KVM fix switches from follow_pfn() to follow_pte() in order to grab the page protections along with the PFN. Fixes: bd2fae8da794 ("KVM: do not assume PTE is writable after follow_pfn") Cc: David Stevens <stevensd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: kvm@vger.kernel.org Signed-off-by: Sean Christopherson <seanjc@google.com> --- Paolo, maybe you can squash this with the appropriate acks? mm/memory.c | 1 + 1 file changed, 1 insertion(+)