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s390/archrandom: Reconsider s390 arch random implementation 

The reworked version of the random device driver now calls
the arch_get_random_* functions on a very high frequency.
It does about 100.000 calls to arch_get_random_long for
providing 10 MB via /dev/urandom. Each invocation was
fetching entropy from the hardware random generator which
has a rate limit of about 4 MB/s. As the trng invocation
waits until enough entropy is gathered, the random device
driver is slowed down dramatically.

The s390 true random generator is not designed for such
a high rate. The TRNG is more designed to be used together
with the arch_get_random_seed_* functions. This is similar
to the way how powerpc has implemented their arch random
functionality.

This patch removes the invocations of the s390 TRNG for
arch_get_random_long() and arch_get_random_int() but leaving
the invocations for arch_get_random_seed_long() and
arch_get_random_seed_int(). So the s390 arch random
implementation now contributes high quality entropy to
the kernel random device for reseeding.

Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
This commit is contained in:
Harald Freudenberger 2017-10-27 15:53:49 +02:00 committed by Heiko Carstens
parent 48070c7305
commit f44fa88745
1 changed files with 13 additions and 13 deletions
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26
arch/s390/include/asm/archrandom.h
View File

@ -27,26 +27,27 @@ static void s390_arch_random_generate(u8 *buf, unsigned int nbytes)
static inline bool arch_has_random(void)
{
if (static_branch_likely(&s390_arch_random_available))
return true;
return false;
}
static inline bool arch_has_random_seed(void)
{
return arch_has_random();
if (static_branch_likely(&s390_arch_random_available))
return true;
return false;
}
static inline bool arch_get_random_long(unsigned long *v)
{
if (static_branch_likely(&s390_arch_random_available)) {
s390_arch_random_generate((u8 *)v, sizeof(*v));
return true;
}
return false;
}
static inline bool arch_get_random_int(unsigned int *v)
{
return false;
}
static inline bool arch_get_random_seed_long(unsigned long *v)
{
if (static_branch_likely(&s390_arch_random_available)) {
s390_arch_random_generate((u8 *)v, sizeof(*v));
@ -55,14 +56,13 @@ static inline bool arch_get_random_int(unsigned int *v)
return false;
}
static inline bool arch_get_random_seed_long(unsigned long *v)
{
return arch_get_random_long(v);
}
static inline bool arch_get_random_seed_int(unsigned int *v)
{
return arch_get_random_int(v);
if (static_branch_likely(&s390_arch_random_available)) {
s390_arch_random_generate((u8 *)v, sizeof(*v));
return true;
}
return false;
}
#endif /* CONFIG_ARCH_RANDOM */