s390/cpumf: Improve guest detection heuristics (b1685ab9) · Commits · 戴 / test

commit ("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>

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;

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