Commit ea678ac6 authored by Naveen N. Rao's avatar Naveen N. Rao Committed by Michael Ellerman

powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths

We have some C code that we call into from real mode where we cannot
take any exceptions. Though the C functions themselves are mostly safe,
if these functions are traced, there is a possibility that we may take
an exception. For instance, in certain conditions, the ftrace code uses
WARN(), which uses a 'trap' to do its job.

For such scenarios, introduce a new field in paca 'ftrace_enabled',
which is checked on ftrace entry before continuing. This field can then
be set to zero to disable/pause ftrace, and set to a non-zero value to
resume ftrace.
Signed-off-by: default avatarNaveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 6da6c0db
......@@ -223,6 +223,7 @@ struct paca_struct {
u8 hmi_event_available; /* HMI event is available */
u8 hmi_p9_special_emu; /* HMI P9 special emulation */
#endif
u8 ftrace_enabled; /* Hard disable ftrace */
/* Stuff for accurate time accounting */
struct cpu_accounting_data accounting;
......
......@@ -180,6 +180,7 @@ int main(void)
OFFSET(PACAKMSR, paca_struct, kernel_msr);
OFFSET(PACAIRQSOFTMASK, paca_struct, irq_soft_mask);
OFFSET(PACAIRQHAPPENED, paca_struct, irq_happened);
OFFSET(PACA_FTRACE_ENABLED, paca_struct, ftrace_enabled);
#ifdef CONFIG_PPC_BOOK3S
OFFSET(PACACONTEXTID, paca_struct, mm_ctx_id);
#ifdef CONFIG_PPC_MM_SLICES
......
......@@ -252,6 +252,9 @@ static void cpu_ready_for_interrupts(void)
/* Set IR and DR in PACA MSR */
get_paca()->kernel_msr = MSR_KERNEL;
/* We are now ok to enable ftrace */
get_paca()->ftrace_enabled = 1;
}
unsigned long spr_default_dscr = 0;
......
......@@ -47,6 +47,12 @@ _GLOBAL(ftrace_caller)
/* Save all gprs to pt_regs */
SAVE_GPR(0, r1)
SAVE_10GPRS(2, r1)
/* Ok to continue? */
lbz r3, PACA_FTRACE_ENABLED(r13)
cmpdi r3, 0
beq ftrace_no_trace
SAVE_10GPRS(12, r1)
SAVE_10GPRS(22, r1)
......@@ -168,6 +174,14 @@ _GLOBAL(ftrace_graph_stub)
_GLOBAL(ftrace_stub)
blr
ftrace_no_trace:
mflr r3
mtctr r3
REST_GPR(3, r1)
addi r1, r1, SWITCH_FRAME_SIZE
mtlr r0
bctr
#ifdef CONFIG_LIVEPATCH
/*
* This function runs in the mcount context, between two functions. As
......
......@@ -16,6 +16,10 @@
#ifdef CONFIG_DYNAMIC_FTRACE
_GLOBAL_TOC(ftrace_caller)
lbz r3, PACA_FTRACE_ENABLED(r13)
cmpdi r3, 0
beqlr
/* Taken from output of objdump from lib64/glibc */
mflr r3
ld r11, 0(r1)
......
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