[RFC git pull] tracing, x86, mmiotrace fixes

From: Ingo Molnar
Date: Tue Mar 03 2009 - 16:16:37 EST


Linus,

Please consider pulling the latest tracing/mmiotrace git tree
from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git tracing/mmiotrace

The built-in mmiotrace code got some serious testing and usage
from the Nouveau freedesktop.org people - resulting in a number
of fixes to this debugging/tracing facility.

The fixes are technically late but they are strictly isolated to
the mmiotrace files only, so i thought we could apply them.

Thanks,

Ingo

------------------>
Pekka Paalanen (5):
x86: count errors in testmmiotrace.ko
x86: add far read test to testmmiotrace
x86 mmiotrace: fix save/restore page table state
x86 mmiotrace: split set_page_presence()
x86 mmiotrace: fix race with release_kmmio_fault_page()

Stuart Bennett (2):
x86 mmiotrace: WARN_ONCE if dis/arming a page fails
x86 mmiotrace: improve handling of secondary faults


arch/x86/mm/kmmio.c | 149 +++++++++++++++++++++++++++---------------
arch/x86/mm/testmmiotrace.c | 70 ++++++++++++++++----
2 files changed, 153 insertions(+), 66 deletions(-)

diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c
index 93d8203..9f20503 100644
--- a/arch/x86/mm/kmmio.c
+++ b/arch/x86/mm/kmmio.c
@@ -32,11 +32,14 @@ struct kmmio_fault_page {
struct list_head list;
struct kmmio_fault_page *release_next;
unsigned long page; /* location of the fault page */
+ bool old_presence; /* page presence prior to arming */
+ bool armed;

/*
* Number of times this page has been registered as a part
* of a probe. If zero, page is disarmed and this may be freed.
- * Used only by writers (RCU).
+ * Used only by writers (RCU) and post_kmmio_handler().
+ * Protected by kmmio_lock, when linked into kmmio_page_table.
*/
int count;
};
@@ -105,57 +108,85 @@ static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
return NULL;
}

-static void set_page_present(unsigned long addr, bool present,
- unsigned int *pglevel)
+static void set_pmd_presence(pmd_t *pmd, bool present, bool *old)
+{
+ pmdval_t v = pmd_val(*pmd);
+ *old = !!(v & _PAGE_PRESENT);
+ v &= ~_PAGE_PRESENT;
+ if (present)
+ v |= _PAGE_PRESENT;
+ set_pmd(pmd, __pmd(v));
+}
+
+static void set_pte_presence(pte_t *pte, bool present, bool *old)
+{
+ pteval_t v = pte_val(*pte);
+ *old = !!(v & _PAGE_PRESENT);
+ v &= ~_PAGE_PRESENT;
+ if (present)
+ v |= _PAGE_PRESENT;
+ set_pte_atomic(pte, __pte(v));
+}
+
+static int set_page_presence(unsigned long addr, bool present, bool *old)
{
- pteval_t pteval;
- pmdval_t pmdval;
unsigned int level;
- pmd_t *pmd;
pte_t *pte = lookup_address(addr, &level);

if (!pte) {
pr_err("kmmio: no pte for page 0x%08lx\n", addr);
- return;
+ return -1;
}

- if (pglevel)
- *pglevel = level;
-
switch (level) {
case PG_LEVEL_2M:
- pmd = (pmd_t *)pte;
- pmdval = pmd_val(*pmd) & ~_PAGE_PRESENT;
- if (present)
- pmdval |= _PAGE_PRESENT;
- set_pmd(pmd, __pmd(pmdval));
+ set_pmd_presence((pmd_t *)pte, present, old);
break;
-
case PG_LEVEL_4K:
- pteval = pte_val(*pte) & ~_PAGE_PRESENT;
- if (present)
- pteval |= _PAGE_PRESENT;
- set_pte_atomic(pte, __pte(pteval));
+ set_pte_presence(pte, present, old);
break;
-
default:
pr_err("kmmio: unexpected page level 0x%x.\n", level);
- return;
+ return -1;
}

__flush_tlb_one(addr);
+ return 0;
}

-/** Mark the given page as not present. Access to it will trigger a fault. */
-static void arm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
+/*
+ * Mark the given page as not present. Access to it will trigger a fault.
+ *
+ * Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the
+ * protection is ignored here. RCU read lock is assumed held, so the struct
+ * will not disappear unexpectedly. Furthermore, the caller must guarantee,
+ * that double arming the same virtual address (page) cannot occur.
+ *
+ * Double disarming on the other hand is allowed, and may occur when a fault
+ * and mmiotrace shutdown happen simultaneously.
+ */
+static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
{
- set_page_present(page & PAGE_MASK, false, pglevel);
+ int ret;
+ WARN_ONCE(f->armed, KERN_ERR "kmmio page already armed.\n");
+ if (f->armed) {
+ pr_warning("kmmio double-arm: page 0x%08lx, ref %d, old %d\n",
+ f->page, f->count, f->old_presence);
+ }
+ ret = set_page_presence(f->page, false, &f->old_presence);
+ WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", f->page);
+ f->armed = true;
+ return ret;
}

-/** Mark the given page as present. */
-static void disarm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
+/** Restore the given page to saved presence state. */
+static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
{
- set_page_present(page & PAGE_MASK, true, pglevel);
+ bool tmp;
+ int ret = set_page_presence(f->page, f->old_presence, &tmp);
+ WARN_ONCE(ret < 0,
+ KERN_ERR "kmmio disarming 0x%08lx failed.\n", f->page);
+ f->armed = false;
}

/*
@@ -202,28 +233,32 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)

ctx = &get_cpu_var(kmmio_ctx);
if (ctx->active) {
- disarm_kmmio_fault_page(faultpage->page, NULL);
if (addr == ctx->addr) {
/*
- * On SMP we sometimes get recursive probe hits on the
- * same address. Context is already saved, fall out.
+ * A second fault on the same page means some other
+ * condition needs handling by do_page_fault(), the
+ * page really not being present is the most common.
*/
- pr_debug("kmmio: duplicate probe hit on CPU %d, for "
- "address 0x%08lx.\n",
- smp_processor_id(), addr);
- ret = 1;
- goto no_kmmio_ctx;
- }
- /*
- * Prevent overwriting already in-flight context.
- * This should not happen, let's hope disarming at least
- * prevents a panic.
- */
- pr_emerg("kmmio: recursive probe hit on CPU %d, "
+ pr_debug("kmmio: secondary hit for 0x%08lx CPU %d.\n",
+ addr, smp_processor_id());
+
+ if (!faultpage->old_presence)
+ pr_info("kmmio: unexpected secondary hit for "
+ "address 0x%08lx on CPU %d.\n", addr,
+ smp_processor_id());
+ } else {
+ /*
+ * Prevent overwriting already in-flight context.
+ * This should not happen, let's hope disarming at
+ * least prevents a panic.
+ */
+ pr_emerg("kmmio: recursive probe hit on CPU %d, "
"for address 0x%08lx. Ignoring.\n",
smp_processor_id(), addr);
- pr_emerg("kmmio: previous hit was at 0x%08lx.\n",
- ctx->addr);
+ pr_emerg("kmmio: previous hit was at 0x%08lx.\n",
+ ctx->addr);
+ disarm_kmmio_fault_page(faultpage);
+ }
goto no_kmmio_ctx;
}
ctx->active++;
@@ -244,7 +279,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
regs->flags &= ~X86_EFLAGS_IF;

/* Now we set present bit in PTE and single step. */
- disarm_kmmio_fault_page(ctx->fpage->page, NULL);
+ disarm_kmmio_fault_page(ctx->fpage);

/*
* If another cpu accesses the same page while we are stepping,
@@ -275,7 +310,7 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx);

if (!ctx->active) {
- pr_debug("kmmio: spurious debug trap on CPU %d.\n",
+ pr_warning("kmmio: spurious debug trap on CPU %d.\n",
smp_processor_id());
goto out;
}
@@ -283,7 +318,11 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
if (ctx->probe && ctx->probe->post_handler)
ctx->probe->post_handler(ctx->probe, condition, regs);

- arm_kmmio_fault_page(ctx->fpage->page, NULL);
+ /* Prevent racing against release_kmmio_fault_page(). */
+ spin_lock(&kmmio_lock);
+ if (ctx->fpage->count)
+ arm_kmmio_fault_page(ctx->fpage);
+ spin_unlock(&kmmio_lock);

regs->flags &= ~X86_EFLAGS_TF;
regs->flags |= ctx->saved_flags;
@@ -315,20 +354,24 @@ static int add_kmmio_fault_page(unsigned long page)
f = get_kmmio_fault_page(page);
if (f) {
if (!f->count)
- arm_kmmio_fault_page(f->page, NULL);
+ arm_kmmio_fault_page(f);
f->count++;
return 0;
}

- f = kmalloc(sizeof(*f), GFP_ATOMIC);
+ f = kzalloc(sizeof(*f), GFP_ATOMIC);
if (!f)
return -1;

f->count = 1;
f->page = page;
- list_add_rcu(&f->list, kmmio_page_list(f->page));

- arm_kmmio_fault_page(f->page, NULL);
+ if (arm_kmmio_fault_page(f)) {
+ kfree(f);
+ return -1;
+ }
+
+ list_add_rcu(&f->list, kmmio_page_list(f->page));

return 0;
}
@@ -347,7 +390,7 @@ static void release_kmmio_fault_page(unsigned long page,
f->count--;
BUG_ON(f->count < 0);
if (!f->count) {
- disarm_kmmio_fault_page(f->page, NULL);
+ disarm_kmmio_fault_page(f);
f->release_next = *release_list;
*release_list = f;
}
diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c
index ab50a8d..427fd1b 100644
--- a/arch/x86/mm/testmmiotrace.c
+++ b/arch/x86/mm/testmmiotrace.c
@@ -1,5 +1,5 @@
/*
- * Written by Pekka Paalanen, 2008 <pq@xxxxxx>
+ * Written by Pekka Paalanen, 2008-2009 <pq@xxxxxx>
*/
#include <linux/module.h>
#include <linux/io.h>
@@ -9,35 +9,74 @@

static unsigned long mmio_address;
module_param(mmio_address, ulong, 0);
-MODULE_PARM_DESC(mmio_address, "Start address of the mapping of 16 kB.");
+MODULE_PARM_DESC(mmio_address, " Start address of the mapping of 16 kB "
+ "(or 8 MB if read_far is non-zero).");
+
+static unsigned long read_far = 0x400100;
+module_param(read_far, ulong, 0);
+MODULE_PARM_DESC(read_far, " Offset of a 32-bit read within 8 MB "
+ "(default: 0x400100).");
+
+static unsigned v16(unsigned i)
+{
+ return i * 12 + 7;
+}
+
+static unsigned v32(unsigned i)
+{
+ return i * 212371 + 13;
+}

static void do_write_test(void __iomem *p)
{
unsigned int i;
+ pr_info(MODULE_NAME ": write test.\n");
mmiotrace_printk("Write test.\n");
+
for (i = 0; i < 256; i++)
iowrite8(i, p + i);
+
for (i = 1024; i < (5 * 1024); i += 2)
- iowrite16(i * 12 + 7, p + i);
+ iowrite16(v16(i), p + i);
+
for (i = (5 * 1024); i < (16 * 1024); i += 4)
- iowrite32(i * 212371 + 13, p + i);
+ iowrite32(v32(i), p + i);
}

static void do_read_test(void __iomem *p)
{
unsigned int i;
+ unsigned errs[3] = { 0 };
+ pr_info(MODULE_NAME ": read test.\n");
mmiotrace_printk("Read test.\n");
+
for (i = 0; i < 256; i++)
- ioread8(p + i);
+ if (ioread8(p + i) != i)
+ ++errs[0];
+
for (i = 1024; i < (5 * 1024); i += 2)
- ioread16(p + i);
+ if (ioread16(p + i) != v16(i))
+ ++errs[1];
+
for (i = (5 * 1024); i < (16 * 1024); i += 4)
- ioread32(p + i);
+ if (ioread32(p + i) != v32(i))
+ ++errs[2];
+
+ mmiotrace_printk("Read errors: 8-bit %d, 16-bit %d, 32-bit %d.\n",
+ errs[0], errs[1], errs[2]);
}

-static void do_test(void)
+static void do_read_far_test(void __iomem *p)
{
- void __iomem *p = ioremap_nocache(mmio_address, 0x4000);
+ pr_info(MODULE_NAME ": read far test.\n");
+ mmiotrace_printk("Read far test.\n");
+
+ ioread32(p + read_far);
+}
+
+static void do_test(unsigned long size)
+{
+ void __iomem *p = ioremap_nocache(mmio_address, size);
if (!p) {
pr_err(MODULE_NAME ": could not ioremap, aborting.\n");
return;
@@ -45,11 +84,15 @@ static void do_test(void)
mmiotrace_printk("ioremap returned %p.\n", p);
do_write_test(p);
do_read_test(p);
+ if (read_far && read_far < size - 4)
+ do_read_far_test(p);
iounmap(p);
}

static int __init init(void)
{
+ unsigned long size = (read_far) ? (8 << 20) : (16 << 10);
+
if (mmio_address == 0) {
pr_err(MODULE_NAME ": you have to use the module argument "
"mmio_address.\n");
@@ -58,10 +101,11 @@ static int __init init(void)
return -ENXIO;
}

- pr_warning(MODULE_NAME ": WARNING: mapping 16 kB @ 0x%08lx "
- "in PCI address space, and writing "
- "rubbish in there.\n", mmio_address);
- do_test();
+ pr_warning(MODULE_NAME ": WARNING: mapping %lu kB @ 0x%08lx in PCI "
+ "address space, and writing 16 kB of rubbish in there.\n",
+ size >> 10, mmio_address);
+ do_test(size);
+ pr_info(MODULE_NAME ": All done.\n");
return 0;
}

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