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Message-ID: <0db8b45d-8f7d-46bc-8739-c167c086bcfc@lucifer.local>
Date: Tue, 16 May 2023 19:37:23 +0100
From: Lorenzo Stoakes <lstoakes@...il.com>
To: Anders Roxell <anders.roxell@...aro.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>,
David Hildenbrand <david@...hat.com>,
linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
linux-s390@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-perf-users@...r.kernel.org,
linux-security-module@...r.kernel.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Eric Biederman <ebiederm@...ssion.com>,
Kees Cook <keescook@...omium.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
Kentaro Takeda <takedakn@...data.co.jp>,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
Paul Moore <paul@...l-moore.com>,
James Morris <jmorris@...ei.org>,
"Serge E . Hallyn" <serge@...lyn.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Jens Axboe <axboe@...nel.dk>,
Pavel Begunkov <asml.silence@...il.com>,
Jason Gunthorpe <jgg@...pe.ca>,
John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v5 3/6] mm/gup: remove vmas parameter from
get_user_pages_remote()
On Tue, May 16, 2023 at 11:49:19AM +0200, Anders Roxell wrote:
> On 2023-05-14 22:26, Lorenzo Stoakes wrote:
> > The only instances of get_user_pages_remote() invocations which used the
> > vmas parameter were for a single page which can instead simply look up the
> > VMA directly. In particular:-
> >
> > - __update_ref_ctr() looked up the VMA but did nothing with it so we simply
> > remove it.
> >
> > - __access_remote_vm() was already using vma_lookup() when the original
> > lookup failed so by doing the lookup directly this also de-duplicates the
> > code.
> >
> > We are able to perform these VMA operations as we already hold the
> > mmap_lock in order to be able to call get_user_pages_remote().
> >
> > As part of this work we add get_user_page_vma_remote() which abstracts the
> > VMA lookup, error handling and decrementing the page reference count should
> > the VMA lookup fail.
> >
> > This forms part of a broader set of patches intended to eliminate the vmas
> > parameter altogether.
> >
> > Reviewed-by: Catalin Marinas <catalin.marinas@....com> (for arm64)
> > Acked-by: David Hildenbrand <david@...hat.com>
> > Reviewed-by: Janosch Frank <frankja@...ux.ibm.com> (for s390)
> > Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
> > ---
> > arch/arm64/kernel/mte.c | 17 +++++++++--------
> > arch/s390/kvm/interrupt.c | 2 +-
> > fs/exec.c | 2 +-
> > include/linux/mm.h | 34 +++++++++++++++++++++++++++++++---
> > kernel/events/uprobes.c | 13 +++++--------
> > mm/gup.c | 12 ++++--------
> > mm/memory.c | 14 +++++++-------
> > mm/rmap.c | 2 +-
> > security/tomoyo/domain.c | 2 +-
> > virt/kvm/async_pf.c | 3 +--
> > 10 files changed, 61 insertions(+), 40 deletions(-)
> >
>
> [...]
>
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 146bb94764f8..63632a5eafc1 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -5590,7 +5590,6 @@ EXPORT_SYMBOL_GPL(generic_access_phys);
> > int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
> > int len, unsigned int gup_flags)
> > {
> > - struct vm_area_struct *vma;
> > void *old_buf = buf;
> > int write = gup_flags & FOLL_WRITE;
> >
> > @@ -5599,13 +5598,15 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
> >
> > /* ignore errors, just check how much was successfully transferred */
> > while (len) {
> > - int bytes, ret, offset;
> > + int bytes, offset;
> > void *maddr;
> > - struct page *page = NULL;
> > + struct vm_area_struct *vma;
> > + struct page *page = get_user_page_vma_remote(mm, addr,
> > + gup_flags, &vma);
> > +
> > + if (IS_ERR_OR_NULL(page)) {
> > + int ret = 0;
>
> I see the warning below when building without CONFIG_HAVE_IOREMAP_PROT set.
>
> make --silent --keep-going --jobs=32 \
> O=/home/anders/.cache/tuxmake/builds/1244/build ARCH=arm \
> CROSS_COMPILE=arm-linux-gnueabihf- /home/anders/src/kernel/next/mm/memory.c: In function '__access_remote_vm':
> /home/anders/src/kernel/next/mm/memory.c:5608:29: warning: unused variable 'ret' [-Wunused-variable]
> 5608 | int ret = 0;
> | ^~~
>
Ah damn, nice spot thanks!
>
> >
> > - ret = get_user_pages_remote(mm, addr, 1,
> > - gup_flags, &page, &vma, NULL);
> > - if (ret <= 0) {
> > #ifndef CONFIG_HAVE_IOREMAP_PROT
> > break;
> > #else
> > @@ -5613,7 +5614,6 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
> > * Check if this is a VM_IO | VM_PFNMAP VMA, which
> > * we can access using slightly different code.
> > */
> > - vma = vma_lookup(mm, addr);
> > if (!vma)
> > break;
> > if (vma->vm_ops && vma->vm_ops->access)
>
> Cheers,
> Anders
I enclose a -fix patch for this below:-
----8<----
>From 6a4bb033a1ec60920e4945e7e063443f91489d06 Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lstoakes@...il.com>
Date: Tue, 16 May 2023 19:16:22 +0100
Subject: [PATCH] mm/gup: remove vmas parameter from get_user_pages_remote()
Fix unused variable warning as reported by Anders Roxell.
Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
---
mm/memory.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 63632a5eafc1..b1b25e61294a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5605,11 +5605,11 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
gup_flags, &vma);
if (IS_ERR_OR_NULL(page)) {
- int ret = 0;
-
#ifndef CONFIG_HAVE_IOREMAP_PROT
break;
#else
+ int ret = 0;
+
/*
* Check if this is a VM_IO | VM_PFNMAP VMA, which
* we can access using slightly different code.
--
2.40.1
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