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Message-Id: <20220128131006.67712-17-michel@lespinasse.org>
Date: Fri, 28 Jan 2022 05:09:47 -0800
From: Michel Lespinasse <michel@...pinasse.org>
To: Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Cc: kernel-team@...com, Laurent Dufour <ldufour@...ux.ibm.com>,
Jerome Glisse <jglisse@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Michal Hocko <mhocko@...e.com>,
Vlastimil Babka <vbabka@...e.cz>,
Davidlohr Bueso <dave@...olabs.net>,
Matthew Wilcox <willy@...radead.org>,
Liam Howlett <liam.howlett@...cle.com>,
Rik van Riel <riel@...riel.com>,
Paul McKenney <paulmck@...nel.org>,
Song Liu <songliubraving@...com>,
Suren Baghdasaryan <surenb@...gle.com>,
Minchan Kim <minchan@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
David Rientjes <rientjes@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Andy Lutomirski <luto@...nel.org>,
Michel Lespinasse <michel@...pinasse.org>
Subject: [PATCH v2 16/35] mm: implement speculative handling in __handle_mm_fault().
The speculative path calls speculative_page_walk_begin() before walking
the page table tree to prevent page table reclamation. The logic is
otherwise similar to the non-speculative path, but with additional
restrictions: in the speculative path, we do not handle huge pages or
wiring new pages tables.
Signed-off-by: Michel Lespinasse <michel@...pinasse.org>
---
include/linux/mm.h | 6 ++++
mm/memory.c | 77 ++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 81 insertions(+), 2 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6f7712179503..2e2122bd3da3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -483,6 +483,10 @@ struct vm_fault {
};
enum fault_flag flags; /* FAULT_FLAG_xxx flags
* XXX: should really be 'const' */
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ unsigned long seq;
+ pmd_t orig_pmd;
+#endif
pmd_t *pmd; /* Pointer to pmd entry matching
* the 'address' */
pud_t *pud; /* Pointer to pud entry matching
@@ -490,9 +494,11 @@ struct vm_fault {
*/
union {
pte_t orig_pte; /* Value of PTE at the time of fault */
+#ifndef CONFIG_SPECULATIVE_PAGE_FAULT
pmd_t orig_pmd; /* Value of PMD at the time of fault,
* used by PMD fault only.
*/
+#endif
};
struct page *cow_page; /* Page handler may use for COW fault */
diff --git a/mm/memory.c b/mm/memory.c
index 37a4b92bd4bf..d0db10bd5bee 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4581,7 +4581,7 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
* return value. See filemap_fault() and __folio_lock_or_retry().
*/
static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
- unsigned long address, unsigned int flags)
+ unsigned long address, unsigned int flags, unsigned long seq)
{
struct vm_fault vmf = {
.vma = vma,
@@ -4596,6 +4596,79 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
p4d_t *p4d;
vm_fault_t ret;
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ if (flags & FAULT_FLAG_SPECULATIVE) {
+ pgd_t pgdval;
+ p4d_t p4dval;
+ pud_t pudval;
+
+ vmf.seq = seq;
+
+ speculative_page_walk_begin();
+ pgd = pgd_offset(mm, address);
+ pgdval = READ_ONCE(*pgd);
+ if (pgd_none(pgdval) || unlikely(pgd_bad(pgdval)))
+ goto spf_fail;
+
+ p4d = p4d_offset(pgd, address);
+ p4dval = READ_ONCE(*p4d);
+ if (p4d_none(p4dval) || unlikely(p4d_bad(p4dval)))
+ goto spf_fail;
+
+ vmf.pud = pud_offset(p4d, address);
+ pudval = READ_ONCE(*vmf.pud);
+ if (pud_none(pudval) || unlikely(pud_bad(pudval)) ||
+ unlikely(pud_trans_huge(pudval)) ||
+ unlikely(pud_devmap(pudval)))
+ goto spf_fail;
+
+ vmf.pmd = pmd_offset(vmf.pud, address);
+ vmf.orig_pmd = READ_ONCE(*vmf.pmd);
+
+ /*
+ * pmd_none could mean that a hugepage collapse is in
+ * progress in our back as collapse_huge_page() mark
+ * it before invalidating the pte (which is done once
+ * the IPI is catched by all CPU and we have interrupt
+ * disabled). For this reason we cannot handle THP in
+ * a speculative way since we can't safely identify an
+ * in progress collapse operation done in our back on
+ * that PMD.
+ */
+ if (unlikely(pmd_none(vmf.orig_pmd) ||
+ is_swap_pmd(vmf.orig_pmd) ||
+ pmd_trans_huge(vmf.orig_pmd) ||
+ pmd_devmap(vmf.orig_pmd)))
+ goto spf_fail;
+
+ /*
+ * The above does not allocate/instantiate page-tables because
+ * doing so would lead to the possibility of instantiating
+ * page-tables after free_pgtables() -- and consequently
+ * leaking them.
+ *
+ * The result is that we take at least one non-speculative
+ * fault per PMD in order to instantiate it.
+ */
+
+ vmf.pte = pte_offset_map(vmf.pmd, address);
+ vmf.orig_pte = READ_ONCE(*vmf.pte);
+ barrier();
+ if (pte_none(vmf.orig_pte)) {
+ pte_unmap(vmf.pte);
+ vmf.pte = NULL;
+ }
+
+ speculative_page_walk_end();
+
+ return handle_pte_fault(&vmf);
+
+ spf_fail:
+ speculative_page_walk_end();
+ return VM_FAULT_RETRY;
+ }
+#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */
+
pgd = pgd_offset(mm, address);
p4d = p4d_alloc(mm, pgd, address);
if (!p4d)
@@ -4815,7 +4888,7 @@ vm_fault_t do_handle_mm_fault(struct vm_area_struct *vma,
if (unlikely(is_vm_hugetlb_page(vma)))
ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
else
- ret = __handle_mm_fault(vma, address, flags);
+ ret = __handle_mm_fault(vma, address, flags, seq);
if (flags & FAULT_FLAG_USER) {
mem_cgroup_exit_user_fault();
--
2.20.1
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