The patch titled
Subject: kvm: explicitly set FOLL_HONOR_NUMA_FAULT in hva_to_pfn_slow()
has been added to the -mm mm-unstable branch. Its filename is
kvm-explicitly-set-foll_honor_numa_fault-in-hva_to_pfn_slow.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kvm-explicitly-set-foll_honor_numa_fault-in-hva_to_pfn_slow.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: kvm: explicitly set FOLL_HONOR_NUMA_FAULT in hva_to_pfn_slow()
Date: Thu, 3 Aug 2023 16:32:04 +0200
KVM is *the* case we know that really wants to honor NUMA hinting falls.
As we want to stop setting FOLL_HONOR_NUMA_FAULT implicitly, set
FOLL_HONOR_NUMA_FAULT whenever we might obtain pages on behalf of a VCPU
to map them into a secondary MMU, and add a comment why.
Do that unconditionally in hva_to_pfn_slow() when calling
get_user_pages_unlocked().
kvmppc_book3s_instantiate_page(), hva_to_pfn_fast() and
gfn_to_page_many_atomic() are similarly used to map pages into a
secondary MMU. However, FOLL_WRITE and get_user_page_fast_only() always
implicitly honor NUMA hinting faults -- as documented for
FOLL_HONOR_NUMA_FAULT -- so we can limit this change to a single location
for now.
Don't set it in check_user_page_hwpoison(), where we really only want to
check if the mapped page is HW-poisoned.
We won't set it for other KVM users of get_user_pages()/pin_user_pages()
* arch/powerpc/kvm/book3s_64_mmu_hv.c: not used to map pages into a
secondary MMU.
* arch/powerpc/kvm/e500_mmu.c: only used on shared TLB pages with userspace
* arch/s390/kvm/*: s390x only supports a single NUMA node either way
* arch/x86/kvm/svm/sev.c: not used to map pages into a secondary MMU.
This is a preparation for making FOLL_HONOR_NUMA_FAULT no longer
implicitly be set by get_user_pages() and friends.
Link: https://lkml.kernel.org/r/20230803143208.383663-4-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: liubo <liubo254@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
virt/kvm/kvm_main.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
--- a/virt/kvm/kvm_main.c~kvm-explicitly-set-foll_honor_numa_fault-in-hva_to_pfn_slow
+++ a/virt/kvm/kvm_main.c
@@ -2517,7 +2517,18 @@ static bool hva_to_pfn_fast(unsigned lon
static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
bool interruptible, bool *writable, kvm_pfn_t *pfn)
{
- unsigned int flags = FOLL_HWPOISON;
+ /*
+ * When a VCPU accesses a page that is not mapped into the secondary
+ * MMU, we lookup the page using GUP to map it, so the guest VCPU can
+ * make progress. We always want to honor NUMA hinting faults in that
+ * case, because GUP usage corresponds to memory accesses from the VCPU.
+ * Otherwise, we'd not trigger NUMA hinting faults once a page is
+ * mapped into the secondary MMU and gets accessed by a VCPU.
+ *
+ * Note that get_user_page_fast_only() and FOLL_WRITE for now
+ * implicitly honor NUMA hinting faults and don't need this flag.
+ */
+ unsigned int flags = FOLL_HWPOISON | FOLL_HONOR_NUMA_FAULT;
struct page *page;
int npages;
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-gup-reintroduce-foll_numa-as-foll_honor_numa_fault.patch
smaps-use-vm_normal_page_pmd-instead-of-follow_trans_huge_pmd.patch
mm-memory_hotplug-document-the-signal_pending-check-in-offline_pages.patch
kvm-explicitly-set-foll_honor_numa_fault-in-hva_to_pfn_slow.patch
mm-gup-dont-implicitly-set-foll_honor_numa_fault.patch
pgtable-improve-pte_protnone-comment.patch
selftest-mm-ksm_functional_tests-test-in-mmap_and_merge_range-if-anything-got-merged.patch
selftest-mm-ksm_functional_tests-add-prot_none-test.patch
