[Xen-changelog] [xen master] mm/page_alloc: make bootscrub happen in idle-loop

[p***@xen.org]

commit 0b24ef785379fff7cfb6e240e985f230155b2b12
Author: Sergey Dyasli <***@citrix.com>
AuthorDate: Wed Nov 7 09:34:17 2018 +0100
Commit: Jan Beulich <***@suse.com>
CommitDate: Wed Nov 7 09:34:17 2018 +0100

mm/page_alloc: make bootscrub happen in idle-loop

Scrubbing RAM during boot may take a long time on machines with lots
of RAM. Add 'idle' option to bootscrub which marks all pages dirty
initially so they will eventually be scrubbed in idle-loop on every
online CPU.

It's guaranteed that the allocator will return scrubbed pages by doing
eager scrubbing during allocation (unless MEMF_no_scrub was provided).

Use the new 'idle' option as the default one.

Signed-off-by: Sergey Dyasli <***@citrix.com>
Reviewed-by: Jan Beulich <***@suse.com>
---
docs/misc/xen-command-line.markdown | 9 ++++--
xen/common/page_alloc.c | 61 ++++++++++++++++++++++++++++++++++---
2 files changed, 64 insertions(+), 6 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index 2c7046eb86..9028bcde2e 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -227,14 +227,19 @@ that byte `0x12345678` is bad, you would place `badpage=0x12345` on
Xen's command line.

### bootscrub
-> `= <boolean>`
+> `= idle | <boolean>`

-> Default: `true`
+> Default: `idle`

Scrub free RAM during boot. This is a safety feature to prevent
accidentally leaking sensitive VM data into other VMs if Xen crashes
and reboots.

+In `idle` mode, RAM is scrubbed in background on all CPUs during idle-loop
+with a guarantee that memory allocations always provide scrubbed pages.
+This option reduces boot time on machines with a large amount of RAM while
+still providing security benefits.
+
### bootscrub\_chunk

`= <size>`

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index d29491017e..1aec13e95f 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -161,8 +161,42 @@ string_param("badpage", opt_badpage);
/*
* no-bootscrub -> Free pages are not zeroed during boot.
*/
-static bool_t opt_bootscrub __initdata = 1;
-boolean_param("bootscrub", opt_bootscrub);
+enum bootscrub_mode {
+ BOOTSCRUB_OFF,
+ BOOTSCRUB_ON,
+ BOOTSCRUB_IDLE,
+};
+static enum bootscrub_mode __initdata opt_bootscrub = BOOTSCRUB_IDLE;
+static int __init parse_bootscrub_param(const char *s)
+{
+ /* Interpret 'bootscrub' alone in its positive boolean form */
+ if ( *s == '\0' )
+ {
+ opt_bootscrub = BOOTSCRUB_ON;
+ return 0;
+ }
+
+ switch ( parse_bool(s, NULL) )
+ {
+ case 0:
+ opt_bootscrub = BOOTSCRUB_OFF;
+ break;
+
+ case 1:
+ opt_bootscrub = BOOTSCRUB_ON;
+ break;
+
+ default:
+ if ( !strcmp(s, "idle") )
+ opt_bootscrub = BOOTSCRUB_IDLE;
+ else
+ return -EINVAL;
+ break;
+ }
+
+ return 0;
+}
+custom_param("bootscrub", parse_bootscrub_param);

/*
* bootscrub_chunk -> Amount of bytes to scrub lockstep on non-SMT CPUs
@@ -1726,6 +1760,7 @@ static void init_heap_pages(
struct page_info *pg, unsigned long nr_pages)
{
unsigned long i;
+ bool idle_scrub = false;

/*
* Some pages may not go through the boot allocator (e.g reserved
@@ -1737,6 +1772,9 @@ static void init_heap_pages(
first_valid_mfn = mfn_min(page_to_mfn(pg), first_valid_mfn);
spin_unlock(&heap_lock);

+ if ( system_state < SYS_STATE_active && opt_bootscrub == BOOTSCRUB_IDLE )
+ idle_scrub = true;
+
for ( i = 0; i < nr_pages; i++ )
{
unsigned int nid = phys_to_nid(page_to_maddr(pg+i));
@@ -1763,7 +1801,7 @@ static void init_heap_pages(
nr_pages -= n;
}

- free_heap_pages(pg + i, 0, scrub_debug);
+ free_heap_pages(pg + i, 0, scrub_debug || idle_scrub);
}
}

@@ -2039,8 +2077,23 @@ void __init heap_init_late(void)
*/
setup_low_mem_virq();

- if ( opt_bootscrub )
+ switch ( opt_bootscrub )
+ {
+ default:
+ ASSERT_UNREACHABLE();
+ /* Fall through */
+
+ case BOOTSCRUB_IDLE:
+ printk("Scrubbing free RAM on in background\n");
+ break;
+
+ case BOOTSCRUB_ON:
scrub_heap_pages();
+ break;
+
+ case BOOTSCRUB_OFF:
+ break;
+ }
}


--
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