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s390/cpumf: Improve guest detection heuristics 

commit e22cf8ca6f ("s390/cpumf: rework program parameter setting
to detect guest samples") requires guest changes to get proper
guest/host. We can do better: We can use the primary asn value,
which is set on all Linux variants to compare this with the host
pp value.
We now have the following cases:
1. Guest using PP
host sample:  gpp == 0, asn == hpp --> host
guest sample: gpp != 0 --> guest
2. Guest not using PP
host sample:  gpp == 0, asn == hpp --> host
guest sample: gpp == 0, asn != hpp --> guest

As soon as the host no longer sets CR4, we must back out
this heuristics - let's add a comment in switch_to.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Christian Borntraeger 2016-02-29 16:05:35 +01:00 committed by Martin Schwidefsky
parent 5d7eccecf8
commit b1685ab9bd
2 changed files with 7 additions and 3 deletions
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1
arch/s390/kernel/entry.S
View File

@ -186,6 +186,7 @@ ENTRY(__switch_to)
stg %r5,__LC_THREAD_INFO # store thread info of next
stg %r15,__LC_KERNEL_STACK # store end of kernel stack
lg %r15,__THREAD_ksp(%r1) # load kernel stack of next
/* c4 is used in guest detection: arch/s390/kernel/perf_cpum_sf.c */
lctl %c4,%c4,__TASK_pid(%r3) # load pid to control reg. 4
mvc __LC_CURRENT_PID(4,%r0),__TASK_pid(%r3) # store pid of next
lmg %r6,%r15,__SF_GPRS(%r15) # load gprs of next task

9
arch/s390/kernel/perf_cpum_sf.c
View File

@ -1022,10 +1022,13 @@ static int perf_push_sample(struct perf_event *event, struct sf_raw_sample *sfr)
/*
* A non-zero guest program parameter indicates a guest
* sample.
* Note that some early samples might be misaccounted to
* the host.
* Note that some early samples or samples from guests without
* lpp usage would be misaccounted to the host. We use the asn
* value as a heuristic to detect most of these guest samples.
* If the value differs from the host hpp value, we assume
* it to be a KVM guest.
*/
if (sfr->basic.gpp)
if (sfr->basic.gpp || sfr->basic.prim_asn != (u16) sfr->basic.hpp)
sde_regs->in_guest = 1;
overflow = 0;