From df26c2e87e6cf3ced1fbd589e40d633a6a7f20cb Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Tue, 4 Apr 2017 12:55:11 +0200 Subject: [PATCH] s390/cpumf: simplify detection of guest samples There are three different code levels in regard to the identification of guest samples. They differ in the way the LPP instruction is used. 1) Old kernels without the LPP instruction. The guest program parameter is always zero. 2) Newer kernels load the process pid into the program parameter with LPP. The guest program parameter is non-zero if the guest executes in a process != idle. 3) The latest kernels load ((1UL << 31) | pid) with LPP to make the value non-zero even for the idle task. The guest program parameter is non-zero if the guest is running. All kernels load the process pid to CR4 on context switch. The CPU sampling code uses the value in CR4 to decide between guest and host samples in case the guest program parameter is zero. The three cases: 1) CR4==pid, gpp==0 2) CR4==pid, gpp==pid 3) CR4==pid, gpp==((1UL << 31) | pid) The load-control instruction to load the pid into CR4 is expensive and the goal is to remove it. To distinguish the host CR4 from the guest pid for the idle process the maximum value 0xffff for the PASN is used. This adds a fourth case for a guest OS with an updated kernel: 4) CR4==0xffff, gpp=((1UL << 31) | pid) The host kernel will have CR4==0xffff and will use (gpp!=0 || CR4!==0xffff) to identify guest samples. This works nicely with all 4 cases, the only possible issue would be a guest with an old kernel (gpp==0) and a process pid of 0xffff. Well, don't do that.. Suggested-by: Christian Borntraeger Reviewed-by: Christian Borntraeger Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/entry.S | 4 ---- arch/s390/kernel/head64.S | 2 +- arch/s390/kernel/perf_cpum_sf.c | 7 +++---- 3 files changed, 4 insertions(+), 9 deletions(-) diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index 02f11018e2df..c6cf338c9327 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -189,10 +189,6 @@ ENTRY(__switch_to) stg %r3,__LC_CURRENT # store task struct 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 */ - xc __SF_EMPTY(8,%r15),__SF_EMPTY(%r15) - mvc __SF_EMPTY+4(4,%r15),__TASK_pid(%r3) - lctlg %c4,%c4,__SF_EMPTY(%r15) # 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 TSTMSK __LC_MACHINE_FLAGS,MACHINE_FLAG_LPP diff --git a/arch/s390/kernel/head64.S b/arch/s390/kernel/head64.S index 482d3526e32b..31c91f24e562 100644 --- a/arch/s390/kernel/head64.S +++ b/arch/s390/kernel/head64.S @@ -52,7 +52,7 @@ ENTRY(startup_continue) .quad 0 # cr1: primary space segment table .quad .Lduct # cr2: dispatchable unit control table .quad 0 # cr3: instruction authorization - .quad 0 # cr4: instruction authorization + .quad 0xffff # cr4: instruction authorization .quad .Lduct # cr5: primary-aste origin .quad 0 # cr6: I/O interrupts .quad 0 # cr7: secondary space segment table diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c index 1c0b58545c04..9a4f279d25ca 100644 --- a/arch/s390/kernel/perf_cpum_sf.c +++ b/arch/s390/kernel/perf_cpum_sf.c @@ -1009,8 +1009,8 @@ static int perf_push_sample(struct perf_event *event, struct sf_raw_sample *sfr) * sample. Some early samples or samples from guests without * lpp usage would be misaccounted to the host. We use the asn * value as an addon heuristic to detect most of these guest samples. - * If the value differs from the host hpp value, we assume to be a - * KVM guest. + * If the value differs from 0xffff (the host value), we assume to + * be a KVM guest. */ switch (sfr->basic.CL) { case 1: /* logical partition */ @@ -1020,8 +1020,7 @@ static int perf_push_sample(struct perf_event *event, struct sf_raw_sample *sfr) sde_regs->in_guest = 1; break; default: /* old machine, use heuristics */ - if (sfr->basic.gpp || - sfr->basic.prim_asn != (u16)sfr->basic.hpp) + if (sfr->basic.gpp || sfr->basic.prim_asn != 0xffff) sde_regs->in_guest = 1; break; } -- 2.20.1