[Xen-changelog] [xen staging] use consistent values when consuming runtime-changeable parameters

[p***@xen.org]

commit ee91031be2852b9e132fddbc00a6eee38e6e23fc
Author: Jan Beulich <***@suse.com>
AuthorDate: Wed Oct 31 17:57:19 2018 +0100
Commit: Jan Beulich <***@suse.com>
CommitDate: Wed Oct 31 17:57:19 2018 +0100

use consistent values when consuming runtime-changeable parameters

There's no guarantee that e.g. a switch() control expression's memory
operand(s) get(s) read just once. Guard against the compiler producing
"unexpected" code by sprinkling around some ACCESS_ONCE().

I'm leaving alone opt_conswitch[]: It gets accessed in quite a few
places anyway, and an intermediate change won't have any severe effect
afaict.

Signed-off-by: Jan Beulich <***@suse.com>
Reviewed-by: Andrew Cooper <***@citrix.com>
Reviewed-by: Wei Liu <***@citrix.com>
Acked-by: George Dunlap <***@citrix.com>
---
xen/arch/x86/pv/domain.c | 2 +-
xen/drivers/char/console.c | 13 +++++++------
2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/pv/domain.c b/xen/arch/x86/pv/domain.c
index 4c95bf3c22..7e84b04082 100644
--- a/xen/arch/x86/pv/domain.c
+++ b/xen/arch/x86/pv/domain.c
@@ -256,7 +256,7 @@ int pv_domain_initialise(struct domain *d)
d->arch.pv.xpti = is_hardware_domain(d) ? opt_xpti_hwdom : opt_xpti_domu;

if ( !is_pv_32bit_domain(d) && use_invpcid && cpu_has_pcid )
- switch ( opt_pcid )
+ switch ( ACCESS_ONCE(opt_pcid) )
{
case PCID_OFF:
break;
diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 3b75f7a472..5419493dbf 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -630,16 +630,16 @@ static void __putstr(const char *str)
static int printk_prefix_check(char *p, char **pp)
{
int loglvl = -1;
- int upper_thresh = xenlog_upper_thresh;
- int lower_thresh = xenlog_lower_thresh;
+ int upper_thresh = ACCESS_ONCE(xenlog_upper_thresh);
+ int lower_thresh = ACCESS_ONCE(xenlog_lower_thresh);

while ( (p[0] == '<') && (p[1] != '\0') && (p[2] == '>') )
{
switch ( p[1] )
{
case 'G':
- upper_thresh = xenlog_guest_upper_thresh;
- lower_thresh = xenlog_guest_lower_thresh;
+ upper_thresh = ACCESS_ONCE(xenlog_guest_upper_thresh);
+ lower_thresh = ACCESS_ONCE(xenlog_guest_lower_thresh);
if ( loglvl == -1 )
loglvl = XENLOG_GUEST_DEFAULT;
break;
@@ -690,13 +690,14 @@ static int parse_console_timestamps(const char *s)

static void printk_start_of_line(const char *prefix)
{
+ enum con_timestamp_mode mode = ACCESS_ONCE(opt_con_timestamp_mode);
struct tm tm;
char tstr[32];
uint64_t sec, nsec;

__putstr(prefix);

- switch ( opt_con_timestamp_mode )
+ switch ( mode )
{
case TSM_DATE:
case TSM_DATE_MS:
@@ -704,7 +705,7 @@ static void printk_start_of_line(const char *prefix)

if ( tm.tm_mday == 0 )
/* nothing */;
- else if ( opt_con_timestamp_mode == TSM_DATE )
+ else if ( mode == TSM_DATE )
{
snprintf(tstr, sizeof(tstr), "[%04u-%02u-%02u %02u:%02u:%02u] ",
1900 + tm.tm_year, tm.tm_mon + 1, tm.tm_mday,
--
generated by git-patchbot for /home/xen/git/xen.git#staging