[kvm-unit-tests v3 04/13] powerpc: Abstract H_CEDE calls into a sleep functions

Nicholas Piggin
2023-03-27T12:45:49Z

This consolidates several implementations, and it no longer leaves
MSR[EE] enabled after the decrementer interrupt is handled, but
rather disables it on return.

The handler no longer allows a continuous ticking, but rather dec
has to be re-armed and EE re-enabled (e.g., via H_CEDE hcall) each
time.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
Since v2:
- Comment about DEC interrupt firing [Thomas review]

lib/powerpc/asm/handlers.h | 2 +-
lib/powerpc/asm/ppc_asm.h | 1 +
lib/powerpc/asm/processor.h | 7 ++++++
lib/powerpc/handlers.c | 10 ++++-----
lib/powerpc/processor.c | 43 +++++++++++++++++++++++++++++++++++++
powerpc/sprs.c | 6 +-----
powerpc/tm.c | 20 +----------------
7 files changed, 58 insertions(+), 31 deletions(-)

diff --git a/lib/powerpc/asm/handlers.h b/lib/powerpc/asm/handlers.h
index 64ba727..e4a0cd4 100644
--- a/lib/powerpc/asm/handlers.h
+++ b/lib/powerpc/asm/handlers.h
@@ -3,6 +3,6 @@

#include <asm/ptrace.h>

-void dec_except_handler(struct pt_regs *regs, void *data);
+void dec_handler_oneshot(struct pt_regs *regs, void *data);

#endif /* _ASMPOWERPC_HANDLERS_H_ */
diff --git a/lib/powerpc/asm/ppc_asm.h b/lib/powerpc/asm/ppc_asm.h
index 1b85f6b..6299ff5 100644
--- a/lib/powerpc/asm/ppc_asm.h
+++ b/lib/powerpc/asm/ppc_asm.h
@@ -36,6 +36,7 @@
#endif /* __BYTE_ORDER__ */

/* Machine State Register definitions: */
+#define MSR_EE_BIT 15 /* External Interrupts Enable */
#define MSR_SF_BIT 63 /* 64-bit mode */

#endif /* _ASMPOWERPC_PPC_ASM_H */
diff --git a/lib/powerpc/asm/processor.h b/lib/powerpc/asm/processor.h
index ac001e1..ebfeff2 100644
--- a/lib/powerpc/asm/processor.h
+++ b/lib/powerpc/asm/processor.h
@@ -20,6 +20,8 @@ static inline uint64_t get_tb(void)

extern void delay(uint64_t cycles);
extern void udelay(uint64_t us);
+extern void sleep_tb(uint64_t cycles);
+extern void usleep(uint64_t us);

static inline void mdelay(uint64_t ms)
{
@@ -27,4 +29,9 @@ static inline void mdelay(uint64_t ms)
udelay(1000);
}

+static inline void msleep(uint64_t ms)
+{
+ usleep(ms * 1000);
+}
+
#endif /* _ASMPOWERPC_PROCESSOR_H_ */
diff --git a/lib/powerpc/handlers.c b/lib/powerpc/handlers.c
index c8721e0..296f14f 100644
--- a/lib/powerpc/handlers.c
+++ b/lib/powerpc/handlers.c
@@ -9,15 +9,13 @@
#include <libcflat.h>
#include <asm/handlers.h>
#include <asm/ptrace.h>
+#include <asm/ppc_asm.h>

/*
* Generic handler for decrementer exceptions (0x900)
- * Just reset the decrementer back to the value specified when registering the
- * handler
+ * Return with MSR[EE] disabled.
*/
-void dec_except_handler(struct pt_regs *regs __unused, void *data)
+void dec_handler_oneshot(struct pt_regs *regs, void *data)
{
- uint64_t dec = *((uint64_t *) data);
-
- asm volatile ("mtdec %0" : : "r" (dec));
+ regs->msr &= ~(1UL << MSR_EE_BIT);
}
diff --git a/lib/powerpc/processor.c b/lib/powerpc/processor.c
index 70391aa..f8b7905 100644
--- a/lib/powerpc/processor.c
+++ b/lib/powerpc/processor.c
@@ -10,6 +10,8 @@
#include <asm/ptrace.h>
#include <asm/setup.h>
#include <asm/barrier.h>
+#include <asm/hcall.h>
+#include <asm/handlers.h>

static struct {
void (*func)(struct pt_regs *, void *data);
@@ -66,3 +68,44 @@ void udelay(uint64_t us)
{
delay((us * tb_hz) / 1000000);
}
+
+void sleep_tb(uint64_t cycles)
+{
+ uint64_t start, end, now;
+
+ start = now = get_tb();
+ end = start + cycles;
+
+ while (end > now) {
+ uint64_t left = end - now;
+
+ /* TODO: Could support large decrementer */
+ if (left > 0x7fffffff)
+ left = 0x7fffffff;
+
+ /* DEC won't fire until H_CEDE is called because EE=0 */
+ asm volatile ("mtdec %0" : : "r" (left));
+ handle_exception(0x900, &dec_handler_oneshot, NULL);
+ /*
+ * H_CEDE is called with MSR[EE] clear and enables it as part
+ * of the hcall, returning with EE enabled. The dec interrupt
+ * is then taken immediately and the handler disables EE.
+ *
+ * If H_CEDE returned for any other interrupt than dec
+ * expiring, that is considered an unhandled interrupt and
+ * the test case would be stopped.
+ */
+ if (hcall(H_CEDE) != H_SUCCESS) {
+ printf("H_CEDE failed\n");
+ abort();
+ }
+ handle_exception(0x900, NULL, NULL);
+
+ now = get_tb();
+ }
+}
+
+void usleep(uint64_t us)
+{
+ sleep_tb((us * tb_hz) / 1000000);
+}
diff --git a/powerpc/sprs.c b/powerpc/sprs.c
index 5cc1cd1..ba4ddee 100644
--- a/powerpc/sprs.c
+++ b/powerpc/sprs.c
@@ -254,7 +254,6 @@ int main(int argc, char **argv)
0x1234567890ABCDEFULL, 0xFEDCBA0987654321ULL,
-1ULL,
};
- static uint64_t decr = 0x7FFFFFFF; /* Max value */

for (i = 1; i < argc; i++) {
if (!strcmp(argv[i], "-w")) {
@@ -288,10 +287,7 @@ int main(int argc, char **argv)
if (pause) {
migrate_once();
} else {
- puts("Sleeping...\n");
- handle_exception(0x900, &dec_except_handler, &decr);
- asm volatile ("mtdec %0" : : "r" (0x3FFFFFFF));
- hcall(H_CEDE);
+ msleep(2000);
}

get_sprs(after);
diff --git a/powerpc/tm.c b/powerpc/tm.c
index 65cacdf..7fa9163 100644
--- a/powerpc/tm.c
+++ b/powerpc/tm.c
@@ -48,17 +48,6 @@ static int count_cpus_with_tm(void)
return available;
}

-static int h_cede(void)
-{
- register uint64_t r3 asm("r3") = H_CEDE;
-
- asm volatile ("sc 1" : "+r"(r3) :
- : "r0", "r4", "r5", "r6", "r7", "r8", "r9",
- "r10", "r11", "r12", "xer", "ctr", "cc");
-
- return r3;
-}
-
/*
* Enable transactional memory
* Returns: FALSE - Failure
@@ -95,14 +84,10 @@ static bool enable_tm(void)
static void test_h_cede_tm(int argc, char **argv)
{
int i;
- static uint64_t decr = 0x3FFFFF; /* ~10ms */

if (argc > 2)
report_abort("Unsupported argument: '%s'", argv[2]);

- handle_exception(0x900, &dec_except_handler, &decr);
- asm volatile ("mtdec %0" : : "r" (decr));
-
if (!start_all_cpus(halt, 0))
report_abort("Failed to start secondary cpus");

@@ -120,10 +105,7 @@ static void test_h_cede_tm(int argc, char **argv)
"bf 2,1b" : : : "cr0");

for (i = 0; i < 500; i++) {
- uint64_t rval = h_cede();
-
- if (rval != H_SUCCESS)
- break;
+ msleep(10);
mdelay(5);
}

--
2.37.2