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Commit b1685ab9 authored by Christian Borntraeger's avatar Christian Borntraeger Committed by Martin Schwidefsky
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s390/cpumf: Improve guest detection heuristics 



commit e22cf8ca ("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: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: default avatarHendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 5d7eccec

arch/s390/kernel/entry.S

+1 −0
Original line number Diff line number Diff line
@@ -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

arch/s390/kernel/perf_cpum_sf.c

+6 −3
Original line number Diff line number Diff line
@@ -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;