Re: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE

From: Peter Zijlstra
Date: Fri Aug 24 2018 - 09:14:22 EST

On Fri, Aug 24, 2018 at 10:35:56AM +0200, Peter Zijlstra wrote:

> Anyway, its sorted now; although I'd like to write me a fairly big
> comment in asm-generic/tlb.h about things, before I forget again.

How's something like so? There's a little page_size thingy in this;
mostly because I couldn't be arsed to split it for now.

Will has opinions on the page_size thing; I'll let him explain.

---

arch/Kconfig | 3 +
arch/arm/include/asm/tlb.h | 3 +-
arch/ia64/include/asm/tlb.h | 3 +-
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/tlb.h | 17 ------
arch/s390/include/asm/tlb.h | 4 +-
arch/sh/include/asm/tlb.h | 4 +-
arch/um/include/asm/tlb.h | 4 +-
include/asm-generic/tlb.h | 130 ++++++++++++++++++++++++++++++++++++-----
mm/huge_memory.c | 4 +-
mm/hugetlb.c | 2 +-
mm/madvise.c | 2 +-
mm/memory.c | 9 ++-
13 files changed, 137 insertions(+), 49 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 6801123932a5..053c44703539 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -365,6 +365,9 @@ config HAVE_RCU_TABLE_FREE
config HAVE_RCU_TABLE_INVALIDATE
bool

+config HAVE_MMU_GATHER_PAGE_SIZE
+ bool
+
config ARCH_HAVE_NMI_SAFE_CMPXCHG
bool

diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h
index f854148c8d7c..d644c3c7c6f3 100644
--- a/arch/arm/include/asm/tlb.h
+++ b/arch/arm/include/asm/tlb.h
@@ -286,8 +286,7 @@ tlb_remove_pmd_tlb_entry(struct mmu_gather *tlb, pmd_t *pmdp, unsigned long addr

#define tlb_migrate_finish(mm) do { } while (0)

-#define tlb_remove_check_page_size_change tlb_remove_check_page_size_change
-static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
+static inline void tlb_change_page_size(struct mmu_gather *tlb,
unsigned int page_size)
{
}
diff --git a/arch/ia64/include/asm/tlb.h b/arch/ia64/include/asm/tlb.h
index 516355a774bf..bf8985f5f876 100644
--- a/arch/ia64/include/asm/tlb.h
+++ b/arch/ia64/include/asm/tlb.h
@@ -282,8 +282,7 @@ do { \
#define tlb_remove_huge_tlb_entry(h, tlb, ptep, address) \
tlb_remove_tlb_entry(tlb, ptep, address)

-#define tlb_remove_check_page_size_change tlb_remove_check_page_size_change
-static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
+static inline void tlb_change_page_size(struct mmu_gather *tlb,
unsigned int page_size)
{
}
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index db0b6eebbfa5..4db1072868f7 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -217,6 +217,7 @@ config PPC
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
select HAVE_RCU_TABLE_FREE if SMP
+ select HAVE_MMU_GATHER_PAGE_SIZE
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RELIABLE_STACKTRACE if PPC64 && CPU_LITTLE_ENDIAN
select HAVE_SYSCALL_TRACEPOINTS
diff --git a/arch/powerpc/include/asm/tlb.h b/arch/powerpc/include/asm/tlb.h
index f0e571b2dc7c..b29a67137acf 100644
--- a/arch/powerpc/include/asm/tlb.h
+++ b/arch/powerpc/include/asm/tlb.h
@@ -27,7 +27,6 @@
#define tlb_start_vma(tlb, vma) do { } while (0)
#define tlb_end_vma(tlb, vma) do { } while (0)
#define __tlb_remove_tlb_entry __tlb_remove_tlb_entry
-#define tlb_remove_check_page_size_change tlb_remove_check_page_size_change

extern void tlb_flush(struct mmu_gather *tlb);

@@ -46,22 +45,6 @@ static inline void __tlb_remove_tlb_entry(struct mmu_gather *tlb, pte_t *ptep,
#endif
}

-static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
- unsigned int page_size)
-{
- if (!tlb->page_size)
- tlb->page_size = page_size;
- else if (tlb->page_size != page_size) {
- if (!tlb->fullmm)
- tlb_flush_mmu(tlb);
- /*
- * update the page size after flush for the new
- * mmu_gather.
- */
- tlb->page_size = page_size;
- }
-}
-
#ifdef CONFIG_SMP
static inline int mm_is_core_local(struct mm_struct *mm)
{
diff --git a/arch/s390/include/asm/tlb.h b/arch/s390/include/asm/tlb.h
index 457b7ba0fbb6..cf3d64313740 100644
--- a/arch/s390/include/asm/tlb.h
+++ b/arch/s390/include/asm/tlb.h
@@ -180,9 +180,7 @@ static inline void pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
#define tlb_remove_huge_tlb_entry(h, tlb, ptep, address) \
tlb_remove_tlb_entry(tlb, ptep, address)

-#define tlb_remove_check_page_size_change tlb_remove_check_page_size_change
-static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
- unsigned int page_size)
+static inline void tlb_change_page_size(struct mmu_gather *tlb, unsigned int page_size)
{
}

diff --git a/arch/sh/include/asm/tlb.h b/arch/sh/include/asm/tlb.h
index 77abe192fb43..af7c9d891cf8 100644
--- a/arch/sh/include/asm/tlb.h
+++ b/arch/sh/include/asm/tlb.h
@@ -127,9 +127,7 @@ static inline void tlb_remove_page_size(struct mmu_gather *tlb,
return tlb_remove_page(tlb, page);
}

-#define tlb_remove_check_page_size_change tlb_remove_check_page_size_change
-static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
- unsigned int page_size)
+static inline void tlb_change_page_size(struct mmu_gather *tlb, unsigned int page_size)
{
}

diff --git a/arch/um/include/asm/tlb.h b/arch/um/include/asm/tlb.h
index dce6db147f24..6463f3ab1767 100644
--- a/arch/um/include/asm/tlb.h
+++ b/arch/um/include/asm/tlb.h
@@ -146,9 +146,7 @@ static inline void tlb_remove_page_size(struct mmu_gather *tlb,
#define tlb_remove_huge_tlb_entry(h, tlb, ptep, address) \
tlb_remove_tlb_entry(tlb, ptep, address)

-#define tlb_remove_check_page_size_change tlb_remove_check_page_size_change
-static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
- unsigned int page_size)
+static inline void tlb_change_page_size(struct mmu_gather *tlb, unsigned int page_size)
{
}

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index b3353e21f3b3..d3573ba10068 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -20,6 +20,108 @@
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>

+/*
+ * Generic MMU-gather implementation.
+ *
+ * The mmu_gather data structure is used by the mm code to implement the
+ * correct and efficient ordering of freeing pages and TLB invalidations.
+ *
+ * This correct ordering is:
+ *
+ * 1) unhook page
+ * 2) TLB invalidate page
+ * 3) free page
+ *
+ * That is, we must never free a page before we have ensured there are no live
+ * translations left to it. Otherwise it might be possible to observe (or
+ * worse, change) the page content after it has been reused.
+ *
+ * The mmu_gather API consists of:
+ *
+ * - tlb_gather_mmu() / tlb_finish_mmu(); start and finish a mmu_gather
+ *
+ * Finish in particular will issue a (final) TLB invalidate and free
+ * all (remaining) queued pages.
+ *
+ * - tlb_start_vma() / tlb_end_vma(); marks the start / end of a VMA
+ *
+ * Defaults to flushing at tlb_end_vma() to reset the range; helps when
+ * there's large holes between the VMAs.
+ *
+ * - tlb_remove_page() / __tlb_remove_page()
+ * - tlb_remove_page_size() / __tlb_remove_page_size()
+ *
+ * __tlb_remove_page_size() is the basic primitive that queues a page for
+ * freeing. __tlb_remove_page() assumes PAGE_SIZE. Both will return a
+ * boolean indicating if the queue is (now) full and a call to
+ * tlb_flush_mmu() is required.
+ *
+ * tlb_remove_page() and tlb_remove_page_size() imply the call to
+ * tlb_flush_mmu() when required and has no return value.
+ *
+ * - tlb_change_page_size()
+ *
+ * call before __tlb_remove_page*() to set the current page-size; implies a
+ * possible tlb_flush_mmu() call.
+ *
+ * - tlb_flush_mmu() / tlb_flush_mmu_tlbonly() / tlb_flush_mmu_free()
+ *
+ * tlb_flush_mmu_tlbonly() - does the TLB invalidate (and resets
+ * related state, like the range)
+ *
+ * tlb_flush_mmu_free() - frees the queued pages; make absolutely
+ * sure no additional tlb_remove_page()
+ * calls happen between _tlbonly() and this.
+ *
+ * tlb_flush_mmu() - the above two calls.
+ *
+ * - mmu_gather::fullmm
+ *
+ * A flag set by tlb_gather_mmu() to indicate we're going to free
+ * the entire mm; this allows a number of optimizations.
+ *
+ * XXX list optimizations
+ *
+ * - mmu_gather::need_flush_all
+ *
+ * A flag that can be set by the arch code if it wants to force
+ * flush the entire TLB irrespective of the range. For instance
+ * x86-PAE needs this when changing top-level entries.
+ *
+ * And requires the architecture to provide and implement tlb_flush().
+ *
+ * tlb_flush() may, in addition to the above mentioned mmu_gather fields, make
+ * use of:
+ *
+ * - mmu_gather::start / mmu_gather::end
+ *
+ * which (when !need_flush_all; fullmm will have start = end = ~0UL) provides
+ * the range that needs to be flushed to cover the pages to be freed.
+ *
+ * Additionally there are a few opt-in features:
+ *
+ * HAVE_MMU_GATHER_PAGE_SIZE
+ *
+ * This ensures we call tlb_flush() every time tlb_change_page_size() actually
+ * changes the size and provides mmu_gather::page_size to tlb_flush().
+ *
+ * HAVE_RCU_TABLE_FREE
+ *
+ * This provides tlb_remove_table(), to be used instead of tlb_remove_page()
+ * for page directores (__p*_free_tlb()). This provides separate freeing of
+ * the page-table pages themselves in a semi-RCU fashion (see comment below).
+ * Useful if your architecture doesn't use IPIs for remote TLB invalidates
+ * and therefore doesn't naturally serialize with software page-table walkers.
+ *
+ * HAVE_RCU_TABLE_INVALIDATE
+ *
+ * This makes HAVE_RCU_TABLE_FREE call tlb_flush_mmu_tlbonly() before freeing
+ * the page-table pages. Required if you use HAVE_RCU_TABLE_FREE and your
+ * architecture uses the Linux page-tables natively.
+ *
+ */
+#define HAVE_GENERIC_MMU_GATHER
+
#ifdef CONFIG_HAVE_RCU_TABLE_FREE
/*
* Semi RCU freeing of the page directories.
@@ -87,14 +189,17 @@ struct mmu_gather_batch {
*/
#define MAX_GATHER_BATCH_COUNT (10000UL/MAX_GATHER_BATCH)

-/* struct mmu_gather is an opaque type used by the mm code for passing around
+/*
+ * struct mmu_gather is an opaque type used by the mm code for passing around
* any data needed by arch specific code for tlb_remove_page.
*/
struct mmu_gather {
struct mm_struct *mm;
+
#ifdef CONFIG_HAVE_RCU_TABLE_FREE
struct mmu_table_batch *batch;
#endif
+
unsigned long start;
unsigned long end;
/* we are in the middle of an operation to clear
@@ -103,15 +208,17 @@ struct mmu_gather {
/* we have performed an operation which
* requires a complete flush of the tlb */
need_flush_all : 1;
+#ifdef CONFIG_HAVE_MMU_GATHER_PAGE_SIZE
+ unsigned int page_size;
+#endif

struct mmu_gather_batch *active;
struct mmu_gather_batch local;
struct page *__pages[MMU_GATHER_BUNDLE];
unsigned int batch_count;
- int page_size;
+
};

-#define HAVE_GENERIC_MMU_GATHER

void arch_tlb_gather_mmu(struct mmu_gather *tlb,
struct mm_struct *mm, unsigned long start, unsigned long end);
@@ -170,21 +277,18 @@ static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
return tlb_remove_page_size(tlb, page, PAGE_SIZE);
}

-#ifndef tlb_remove_check_page_size_change
-#define tlb_remove_check_page_size_change tlb_remove_check_page_size_change
-static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
+static inline void tlb_change_page_size(struct mmu_gather *tlb,
unsigned int page_size)
{
- /*
- * We don't care about page size change, just update
- * mmu_gather page size here so that debug checks
- * doesn't throw false warning.
- */
-#ifdef CONFIG_DEBUG_VM
+#ifdef CONFIG_HAVE_MMU_GATHER_PAGE_SIZE
+ if (tlb->page_size && tlb->page_size != page_size) {
+ if (!tlb->fullmm)
+ tlb_flush_mmu(tlb);
+ }
+
tlb->page_size = page_size;
#endif
}
-#endif

/*
* In the case of tlb vma handling, we can optimise these away in the
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 08b544383d74..786758670ba1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1617,7 +1617,7 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
struct mm_struct *mm = tlb->mm;
bool ret = false;

- tlb_remove_check_page_size_change(tlb, HPAGE_PMD_SIZE);
+ tlb_change_page_size(tlb, HPAGE_PMD_SIZE);

ptl = pmd_trans_huge_lock(pmd, vma);
if (!ptl)
@@ -1693,7 +1693,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
pmd_t orig_pmd;
spinlock_t *ptl;

- tlb_remove_check_page_size_change(tlb, HPAGE_PMD_SIZE);
+ tlb_change_page_size(tlb, HPAGE_PMD_SIZE);

ptl = __pmd_trans_huge_lock(pmd, vma);
if (!ptl)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3c21775f196b..8af346b53a79 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3337,7 +3337,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
* This is a hugetlb vma, all the pte entries should point
* to huge page.
*/
- tlb_remove_check_page_size_change(tlb, sz);
+ tlb_change_page_size(tlb, sz);
tlb_start_vma(tlb, vma);
mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
address = start;
diff --git a/mm/madvise.c b/mm/madvise.c
index 4d3c922ea1a1..2a9073c652d2 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -328,7 +328,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
if (pmd_trans_unstable(pmd))
return 0;

- tlb_remove_check_page_size_change(tlb, PAGE_SIZE);
+ tlb_change_page_size(tlb, PAGE_SIZE);
orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
flush_tlb_batched_pending(mm);
arch_enter_lazy_mmu_mode();
diff --git a/mm/memory.c b/mm/memory.c
index 83aef222f11b..2818e00d1aae 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -233,7 +233,9 @@ void arch_tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
#ifdef CONFIG_HAVE_RCU_TABLE_FREE
tlb->batch = NULL;
#endif
+#ifdef CONFIG_HAVE_MMU_GATHER_PAGE_SIZE
tlb->page_size = 0;
+#endif

__tlb_reset_range(tlb);
}
@@ -294,7 +296,10 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_
struct mmu_gather_batch *batch;

VM_BUG_ON(!tlb->end);
+
+#ifdef CONFIG_HAVE_MMU_GATHER_PAGE_SIZE
VM_WARN_ON(tlb->page_size != page_size);
+#endif

batch = tlb->active;
/*
@@ -602,7 +607,7 @@ void free_pgd_range(struct mmu_gather *tlb,
* We add page table cache pages with PAGE_SIZE,
* (see pte_free_tlb()), flush the tlb if we need
*/
- tlb_remove_check_page_size_change(tlb, PAGE_SIZE);
+ tlb_change_page_size(tlb, PAGE_SIZE);
pgd = pgd_offset(tlb->mm, addr);
do {
next = pgd_addr_end(addr, end);
@@ -1293,7 +1298,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
pte_t *pte;
swp_entry_t entry;

- tlb_remove_check_page_size_change(tlb, PAGE_SIZE);
+ tlb_change_page_size(tlb, PAGE_SIZE);
again:
init_rss_vec(rss);
start_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);