[patch V2 05/10] x86/mm/cpa: Add large page preservation statistics

Thomas Gleixner
2018-09-14T13:21:44Z

[-- Attachment #1: x86-mm-cpa--Add-large-page-preservation-statistics.patch --]
[-- Type: text/plain, Size: 5338 bytes --]

The large page preservation mechanism is just magic and provides no
information at all. Add optional statistic output in debugfs so the magic can
be evaluated. Defaults is off.

Output:

1G pages checked: 2
1G pages sameprot: 0
1G pages preserved: 0
2M pages checked: 540
2M pages sameprot: 466
2M pages preserved: 47
4K pages checked: 800770
4K pages set-checked: 7668

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/Kconfig | 8 +++
arch/x86/mm/pageattr.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 105 insertions(+), 2 deletions(-)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1495,6 +1495,14 @@ config X86_DIRECT_GBPAGES
supports them), so don't confuse the user by printing
that we have them enabled.

+config X86_CPA_STATISTICS
+ bool "Enable statistic for Change Page Attribute"
+ depends on DEBUG_FS
+ ---help---
+ Expose statistics about the Change Page Attribute mechanims, which
+ helps to determine the effectivness of preserving large and huge
+ page mappings when mapping protections are changed.
+
config ARCH_HAS_MEM_ENCRYPT
def_bool y

--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -101,6 +101,95 @@ void arch_report_meminfo(struct seq_file
static inline void split_page_count(int level) { }
#endif

+#ifdef CONFIG_X86_CPA_STATISTICS
+
+static unsigned long cpa_1g_checked;
+static unsigned long cpa_1g_sameprot;
+static unsigned long cpa_1g_preserved;
+static unsigned long cpa_2m_checked;
+static unsigned long cpa_2m_sameprot;
+static unsigned long cpa_2m_preserved;
+static unsigned long cpa_4k_checked;
+static unsigned long cpa_4k_install;
+
+static inline void cpa_inc_1g_checked(void)
+{
+ cpa_1g_checked++;
+}
+
+static inline void cpa_inc_2m_checked(void)
+{
+ cpa_2m_checked++;
+}
+
+static inline void cpa_inc_4k_checked(void)
+{
+ cpa_4k_checked++;
+}
+
+static inline void cpa_inc_4k_install(void)
+{
+ cpa_4k_install++;
+}
+
+static inline void cpa_inc_lp_sameprot(int level)
+{
+ if (level == PG_LEVEL_1G)
+ cpa_1g_sameprot++;
+ else
+ cpa_2m_sameprot++;
+}
+
+static inline void cpa_inc_lp_preserved(int level)
+{
+ if (level == PG_LEVEL_1G)
+ cpa_1g_preserved++;
+ else
+ cpa_2m_preserved++;
+}
+
+static int cpastats_show(struct seq_file *m, void *p)
+{
+ seq_printf(m, "1G pages checked: %16lu\n", cpa_1g_checked);
+ seq_printf(m, "1G pages sameprot: %16lu\n", cpa_1g_sameprot);
+ seq_printf(m, "1G pages preserved: %16lu\n", cpa_1g_preserved);
+ seq_printf(m, "2M pages checked: %16lu\n", cpa_2m_checked);
+ seq_printf(m, "2M pages sameprot: %16lu\n", cpa_2m_sameprot);
+ seq_printf(m, "2M pages preserved: %16lu\n", cpa_2m_preserved);
+ seq_printf(m, "4K pages checked: %16lu\n", cpa_4k_checked);
+ seq_printf(m, "4K pages set-checked: %16lu\n", cpa_4k_install);
+ return 0;
+}
+
+static int cpastats_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, cpastats_show, NULL);
+}
+
+static const struct file_operations cpastats_fops = {
+ .open = cpastats_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+static int __init cpa_stats_init(void)
+{
+ debugfs_create_file("cpa_stats", S_IRUSR, arch_debugfs_dir, NULL,
+ &cpastats_fops);
+ return 0;
+}
+late_initcall(cpa_stats_init);
+#else
+static inline void cpa_inc_1g_checked(void) { }
+static inline void cpa_inc_2m_checked(void) { }
+static inline void cpa_inc_4k_checked(void) { }
+static inline void cpa_inc_4k_install(void) { }
+static inline void cpa_inc_lp_sameprot(int level) { }
+static inline void cpa_inc_lp_preserved(int level) { }
+#endif
+
+
static inline int
within(unsigned long addr, unsigned long start, unsigned long end)
{
@@ -660,10 +749,12 @@ static int __should_split_large_page(pte
case PG_LEVEL_2M:
old_prot = pmd_pgprot(*(pmd_t *)kpte);
old_pfn = pmd_pfn(*(pmd_t *)kpte);
+ cpa_inc_2m_checked();
break;
case PG_LEVEL_1G:
old_prot = pud_pgprot(*(pud_t *)kpte);
old_pfn = pud_pfn(*(pud_t *)kpte);
+ cpa_inc_1g_checked();
break;
default:
return -EINVAL;
@@ -728,14 +819,16 @@ static int __should_split_large_page(pte
for (i = 0, addr = lpaddr; i < numpages; i++, addr += PAGE_SIZE, pfn++) {
pgprot_t chk_prot = static_protections(req_prot, addr, pfn, 1,
CPA_DETECT);
-
+ cpa_inc_4k_checked();
if (pgprot_val(chk_prot) != pgprot_val(new_prot))
return 1;
}

/* If there are no changes, return. */
- if (pgprot_val(new_prot) == pgprot_val(old_prot))
+ if (pgprot_val(new_prot) == pgprot_val(old_prot)) {
+ cpa_inc_lp_sameprot(level);
return 0;
+ }

/*
* Verify that the address is aligned and the number of pages
@@ -748,6 +841,7 @@ static int __should_split_large_page(pte
new_pte = pfn_pte(old_pfn, new_prot);
__set_pmd_pte(kpte, address, new_pte);
cpa->flags |= CPA_FLUSHTLB;
+ cpa_inc_lp_preserved(level);
return 0;
}

@@ -1337,6 +1431,7 @@ static int __change_page_attr(struct cpa
pgprot_val(new_prot) &= ~pgprot_val(cpa->mask_clr);
pgprot_val(new_prot) |= pgprot_val(cpa->mask_set);

+ cpa_inc_4k_install();
new_prot = static_protections(new_prot, address, pfn, 1,
CPA_PROTECT);