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Subject[PATCH V2] x86/mm: Split vmalloc_sync_all()
Date
From: Joerg Roedel <jroedel@suse.de>

Git commit 3f8fd02b1bf1 ("mm/vmalloc: Sync unmappings in
__purge_vmap_area_lazy()") introduced a call to vmalloc_sync_all() in
the vunmap() code-path. While this change was necessary to maintain
correctness on x86-32-pae kernels, it also adds additional cycles for
architectures that don't need it.

Specifically on x86-64 with CONFIG_VMAP_STACK=y some people reported
severe performance regressions in micro-benchmarks because it now also
calls the x86-64 implementation of vmalloc_sync_all() on vunmap(). But
the vmalloc_sync_all() implementation on x86-64 is only needed for
newly created mappings.

To avoid the unnecessary work on x86-64 and to gain the performance
back, split up vmalloc_sync_all() into two functions:

* vmalloc_sync_mappings(), and
* vmalloc_sync_unmappings()

Most call-sites to vmalloc_sync_all() only care about new mappings
being synchronized. The only exception is the new call-site
added in the above mentioned commit.

Reported-by: kernel test robot <oliver.sang@intel.com>
Fixes: 3f8fd02b1bf1 ("mm/vmalloc: Sync unmappings in __purge_vmap_area_lazy()")
Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
Changes to initial post:
- Added comments to x86-64 version of
vmalloc_sync_[un]mappings() as suggested by Dave
Hansen.

arch/x86/mm/fault.c | 26 ++++++++++++++++++++++++--
drivers/acpi/apei/ghes.c | 2 +-
include/linux/vmalloc.h | 5 +++--
kernel/notifier.c | 2 +-
mm/nommu.c | 10 +++++++---
mm/vmalloc.c | 11 +++++++----
6 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 9ceacd1156db..94174361f524 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -189,7 +189,7 @@ static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
return pmd_k;
}

-void vmalloc_sync_all(void)
+static void vmalloc_sync(void)
{
unsigned long address;

@@ -216,6 +216,16 @@ void vmalloc_sync_all(void)
}
}

+void vmalloc_sync_mappings(void)
+{
+ vmalloc_sync();
+}
+
+void vmalloc_sync_unmappings(void)
+{
+ vmalloc_sync();
+}
+
/*
* 32-bit:
*
@@ -318,11 +328,23 @@ static void dump_pagetable(unsigned long address)

#else /* CONFIG_X86_64: */

-void vmalloc_sync_all(void)
+void vmalloc_sync_mappings(void)
{
+ /*
+ * 64-bit mappings might allocate new p4d/pud pages
+ * that need to be propagated to all tasks' PGDs.
+ */
sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END);
}

+void vmalloc_sync_unmappings(void)
+{
+ /*
+ * Unmappings never allocate or free p4d/pud pages.
+ * No work is required here.
+ */
+}
+
/*
* 64-bit:
*
diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index 777f6f7122b4..e0d82fab1f44 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -171,7 +171,7 @@ int ghes_estatus_pool_init(int num_ghes)
* New allocation must be visible in all pgd before it can be found by
* an NMI allocating from the pool.
*/
- vmalloc_sync_all();
+ vmalloc_sync_mappings();

rc = gen_pool_add(ghes_estatus_pool, addr, PAGE_ALIGN(len), -1);
if (rc)
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 4e7809408073..decac0790fc1 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -126,8 +126,9 @@ extern int remap_vmalloc_range_partial(struct vm_area_struct *vma,

extern int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
unsigned long pgoff);
-void vmalloc_sync_all(void);
-
+void vmalloc_sync_mappings(void);
+void vmalloc_sync_unmappings(void);
+
/*
* Lowlevel-APIs (not for driver use!)
*/
diff --git a/kernel/notifier.c b/kernel/notifier.c
index d9f5081d578d..157d7c29f720 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -554,7 +554,7 @@ NOKPROBE_SYMBOL(notify_die);

int register_die_notifier(struct notifier_block *nb)
{
- vmalloc_sync_all();
+ vmalloc_sync_mappings();
return atomic_notifier_chain_register(&die_chain, nb);
}
EXPORT_SYMBOL_GPL(register_die_notifier);
diff --git a/mm/nommu.c b/mm/nommu.c
index 99b7ec318824..3b67bd20c2af 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -359,10 +359,14 @@ void vm_unmap_aliases(void)
EXPORT_SYMBOL_GPL(vm_unmap_aliases);

/*
- * Implement a stub for vmalloc_sync_all() if the architecture chose not to
- * have one.
+ * Implement a stub for vmalloc_sync_[un]mapping() if the architecture
+ * chose not to have one.
*/
-void __weak vmalloc_sync_all(void)
+void __weak vmalloc_sync_mappings(void)
+{
+}
+
+void __weak vmalloc_sync_unmappings(void)
{
}

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a3c70e275f4e..c0be707db434 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1259,7 +1259,7 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
* First make sure the mappings are removed from all page-tables
* before they are freed.
*/
- vmalloc_sync_all();
+ vmalloc_sync_unmappings();

/*
* TODO: to calculate a flush range without looping.
@@ -3050,16 +3050,19 @@ int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
EXPORT_SYMBOL(remap_vmalloc_range);

/*
- * Implement a stub for vmalloc_sync_all() if the architecture chose not to
- * have one.
+ * Implement stubs for vmalloc_sync_[un]mappings () if the architecture chose
+ * not to have one.
*
* The purpose of this function is to make sure the vmalloc area
* mappings are identical in all page-tables in the system.
*/
-void __weak vmalloc_sync_all(void)
+void __weak vmalloc_sync_mappings(void)
{
}

+void __weak vmalloc_sync_unmappings(void)
+{
+}

static int f(pte_t *pte, unsigned long addr, void *data)
{
--
2.16.4
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