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Subject[PATCH] x86 mmiotrace: refactor clearing/restore of page presence
Date
* change function names to clear_* from set_*: in reality we only clear
and restore page presence, and never unconditionally set present.
Using clear_*({true, false}, ...) is therefore more honest than
set_*({false, true}, ...)
* upgrade presence storage to pteval_t: doing user-space tracing will
require saving and manipulation of the _PAGE_PROTNONE bit, in addition
to the existing _PAGE_PRESENT changes, and having multiple bools stored
and passed around does not seem optimal

Signed-off-by: Stuart Bennett <stuart@freedesktop.org>
Acked-by: Pekka Paalanen <pq@iki.fi>
---
arch/x86/mm/kmmio.c | 43 ++++++++++++++++++++++---------------------
1 files changed, 22 insertions(+), 21 deletions(-)
diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c
index 6db840e..422f49e 100644
--- a/arch/x86/mm/kmmio.c
+++ b/arch/x86/mm/kmmio.c
@@ -32,7 +32,7 @@ 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 */
+ pteval_t old_presence; /* page presence prior to arming */
bool armed;

/*
@@ -108,49 +108,51 @@ static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
return NULL;
}

-static void set_pmd_presence(pmd_t *pmd, bool present, bool *old)
+static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old)
{
pmdval_t v = pmd_val(*pmd);
- *old = !!(v & _PAGE_PRESENT);
- v &= ~_PAGE_PRESENT;
- if (present)
- v |= _PAGE_PRESENT;
+ if (clear) {
+ *old = v & _PAGE_PRESENT;
+ v &= ~_PAGE_PRESENT;
+ } else /* presume this has been called with clear==true previously */
+ v |= *old;
set_pmd(pmd, __pmd(v));
}

-static void set_pte_presence(pte_t *pte, bool present, bool *old)
+static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
{
pteval_t v = pte_val(*pte);
- *old = !!(v & _PAGE_PRESENT);
- v &= ~_PAGE_PRESENT;
- if (present)
- v |= _PAGE_PRESENT;
+ if (clear) {
+ *old = v & _PAGE_PRESENT;
+ v &= ~_PAGE_PRESENT;
+ } else /* presume this has been called with clear==true previously */
+ v |= *old;
set_pte_atomic(pte, __pte(v));
}

-static int set_page_presence(unsigned long addr, bool present, bool *old)
+static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
{
unsigned int level;
- pte_t *pte = lookup_address(addr, &level);
+ pte_t *pte = lookup_address(f->page, &level);

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

switch (level) {
case PG_LEVEL_2M:
- set_pmd_presence((pmd_t *)pte, present, old);
+ clear_pmd_presence((pmd_t *)pte, clear, &f->old_presence);
break;
case PG_LEVEL_4K:
- set_pte_presence(pte, present, old);
+ clear_pte_presence(pte, clear, &f->old_presence);
break;
default:
pr_err("kmmio: unexpected page level 0x%x.\n", level);
return -1;
}

- __flush_tlb_one(addr);
+ __flush_tlb_one(f->page);
return 0;
}

@@ -171,9 +173,9 @@ static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
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);
+ f->page, f->count, !!f->old_presence);
}
- ret = set_page_presence(f->page, false, &f->old_presence);
+ ret = clear_page_presence(f, true);
WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", f->page);
f->armed = true;
return ret;
@@ -182,8 +184,7 @@ static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
/** Restore the given page to saved presence state. */
static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
{
- bool tmp;
- int ret = set_page_presence(f->page, f->old_presence, &tmp);
+ int ret = clear_page_presence(f, false);
WARN_ONCE(ret < 0,
KERN_ERR "kmmio disarming 0x%08lx failed.\n", f->page);
f->armed = false;
--
1.5.4.4


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