Re: [kvm-unit-tests PATCH V2 4/4] powerpc/tm: Add a test for H_CEDE while tm suspended

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

On Wed, 2016-08-10 at 11:43 +0200, Thomas Huth wrote:
>  Hi,
> 
> thanks for contributing powerpc tests to kvm-unit-tests, that's very
> welcome!
> I've got some remarks / questions on the code, though, see below...
> 
> On 10.08.2016 03:59, Suraj Jitindar Singh wrote:
> > 
> > On Power machines if a guest cedes while a tm transaction is in the
> > suspended state then the checkpointed state of the vcpu may be lost
> > and we
> > lose the cpu in the host.
> > 
> > Add a file for tm tests "powerpc/tm.c" and add a test to check if
> > the fix
> > has been applied to the host kernel. If this fix hasn't been
> > applied then
> > the test will never complete and the cpu will be lost. Otherwise
> > the test
> > should succeed. Since this has the ability to mess things up in the
> > host
> > mark this test as don't run by default.
> > 
> > Based on initial work done by: Cyril Bur <cyril.bur@au1.ibm.com>
> > 
> > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
> Maybe add a reference to the CVE number? (I think there was one,
> wasn't it?)
> 
Yeah there is a CVE, I'll reference it
> > 
> > ---
> >  lib/powerpc/asm/hcall.h |   1 +
> >  powerpc/Makefile.common |   3 +-
> >  powerpc/tm.c            | 176
> > ++++++++++++++++++++++++++++++++++++++++++++++++
> >  powerpc/unittests.cfg   |   6 ++
> >  4 files changed, 185 insertions(+), 1 deletion(-)
> >  create mode 100644 powerpc/tm.c
> > 
> > diff --git a/lib/powerpc/asm/hcall.h b/lib/powerpc/asm/hcall.h
> > index 99bce79..80aa3e3 100644
> > --- a/lib/powerpc/asm/hcall.h
> > +++ b/lib/powerpc/asm/hcall.h
> > @@ -18,6 +18,7 @@
> >  #define H_SET_SPRG0		0x24
> >  #define H_SET_DABR		0x28
> >  #define H_PAGE_INIT		0x2c
> > +#define H_CEDE			0xE0
> >  #define H_PUT_TERM_CHAR		0x58
> >  #define H_RANDOM		0x300
> >  #define H_SET_MODE		0x31C
> > diff --git a/powerpc/Makefile.common b/powerpc/Makefile.common
> > index 677030a..93e4f66 100644
> > --- a/powerpc/Makefile.common
> > +++ b/powerpc/Makefile.common
> > @@ -8,7 +8,8 @@ tests-common = \
> >  	$(TEST_DIR)/selftest.elf \
> >  	$(TEST_DIR)/spapr_hcall.elf \
> >  	$(TEST_DIR)/rtas.elf \
> > -	$(TEST_DIR)/emulator.elf
> > +	$(TEST_DIR)/emulator.elf \
> > +	$(TEST_DIR)/tm.elf
> >  
> >  all: $(TEST_DIR)/boot_rom.bin test_cases
> >  
> > diff --git a/powerpc/tm.c b/powerpc/tm.c
> > new file mode 100644
> > index 0000000..7f675ff
> > --- /dev/null
> > +++ b/powerpc/tm.c
> > @@ -0,0 +1,176 @@
> > +/*
> > + * Transactional Memory Unit Tests
> > + *
> > + * Copyright 2016 Suraj Jitindar Singh, IBM.
> > + *
> > + * This work is licensed under the terms of the GNU LGPL, version
> > 2.
> > + */
> > +#include <libcflat.h>
> > +#include <libfdt/libfdt.h>
> > +#include <devicetree.h>
> > +#include <util.h>
> > +#include <alloc.h>
> > +#include <asm/hcall.h>
> > +#include <asm/ppc_asm.h>
> > +#include <asm/processor.h>
> > +#include <asm/handlers.h>
> > +#include <asm/smp.h>
> > +
> > +#define US_TO_CYCLES(us)	(us << 9)
> That's maybe true for current systems (so it's OK for this specific
> test, I think), but the cleaner way would be to get the
> timebase-frequency from the device tree instead. So I'd like to
> suggest
> that you either add some code to read this value from the device
> tree,
> or add at least an appropriate comment here.
> 
Yeah it makes sense to get this from the device tree, I'll do that.
> > 
> > +/*
> > + * Get decrementer value
> > + */
> > +static uint64_t get_dec(void)
> > +{
> > +	uint64_t dec = 0;
> > +
> > +	asm volatile ( "mfdec %[dec]"	: [dec] "+r" (dec)
> Why "+r"? I think "=r" should be enough here?
Yes, "=" is sufficient
> 
> > 
> > +					:
> > +					:
> You can also omit the empty lines with ":" above.
> 
Will do
> > 
> > +		     );
> > +
> > +	return dec;
> > +}
> > +
> > +/*
> > + * Sleep for <us> micro-seconds (must be less than 4 seconds)
> > + */
> > +static void sleep(uint64_t us)
> Could you please name that function "usleep" instead? The sleep()
> function from the libc is traditionally waiting for seconds, not
> microseconds, so that could help to avoid some confusing if you name
> it
> usleep() instead.
I'll change the name
> 
> > 
> > +{
> > +	uint64_t expire_time, dec, cycles = US_TO_CYCLES(us);
> > +
> > +	if (cycles > 0x7FFFFFFF)
> > +		cycles = 0x7FFFFFFF;
> I'd maybe do an "assert(cycles <= 0x7FFFFFFF)" here instead since
> otherwise, the code is not doing what the caller expected.
That makes sense, will do
> 
> > 
> > +	if (cycles > (dec = get_dec())) {
> It's always easier to read of you put that on two lines:
> 
> 	dec = get_dec();
> 	if (dec < cycles) {
> 		 ...
Ok
> 
> > 
> > +		expire_time = 0x7FFFFFFF + dec - cycles;
> > +		while (get_dec() < dec)
> > +			;
> > +	} else {
> > +		expire_time = dec - cycles;
> > +	}
> > +
> > +	while (get_dec() > expire_time)
> > +		;
> > +}
> > +
> > +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:	0 - Failure
> > + *		1 - Success
> > + */
> > +static bool enable_tm(void)
> > +{
> > +	uint64_t msr = 0;
> > +
> > +	asm volatile ( "mfmsr %[msr]"	: [msr] "+r" (msr)
> That should be "=r" instead of "+r".
Ok
> 
> > 
> > +					:
> > +					:
> > +		     );
> > +
> > +	msr |= (((uint64_t) 1) << 32);
> > +
> > +	asm volatile (	"mtmsrd %1\n\t"
> > +			"mfmsr %0"		: "+r" (msr)
> > +						: "r" (msr)
> I think you should either use "=r" instead of "+r", or skip the
> "r"(msr)
> input parameter, since the "+" modifier already declares it as
> input+output (in the latter case, you've got to change the %1 to %0,
> too, obviously).
Yeah, makes sense
> 
> > 
> > +						:
> > +		     );
> > +
> > +	return !!(msr & (((uint64_t) 1) << 32));
> > +}
> > +
> > +/*
> > + * Test H_CEDE call while transactional memory transaction is
> > suspended
> > + *
> > + * WARNING: This tests for a known vulnerability in which the host
> > may go down.
> > + * Probably best not to run this if your host going down is going
> > to cause
> > + * problems.
> > + *
> > + * If the test passes then your kernel probably has the necessary
> > patch.
> > + * If the test fails then the H_CEDE call was unsuccessful and the
> > + * vulnerability wasn't tested.
> > + * If the test hits the vulnerability then it will never complete
> > or report and
> > + * the qemu process will block indefinately. RCU stalls will be
> > detected on the
> s/indefinately/indefinitely/
> 
Ok
> > 
> > + * cpu and any process scheduled on the lost cpu will also block
> > indefinitely.
> > + */
> > +static void test_h_cede_tm(int argc, char **argv)
> > +{
> > +	bool pass = true;
> > +	int i;
> > +
> > +	if (argc > 2)
> > +		report_abort("Unsupported argument: '%s'",
> > argv[2]);
> > +
> > +	handle_exception(0x900, &dec_except_handler, NULL);
> > +
> > +	if (!start_all_cpus(&halt, 0))
> > +		report_abort("Failed to start secondary cpus");
> > +
> > +	if (!enable_tm())
> > +		report_abort("Failed to enable tm");
> > +
> > +	/*
> > +	 * Begin a transaction and guarantee we are in the suspend
> > state
> > +	 * before continuing
> > +	 */
> > +	asm volatile (	"1: tbegin.\n\t"
> > +			"beq 2f\n\t"
> > +			"tsuspend.\n\t"
> > +			"2: tcheck cr0\n\t"
> > +			"bf 2,1b"		:
> > +						:
> > +						: "cr0"
> > +		     );
> > +
> > +	for (i = 0; i < 500 && pass; i++) {
> > +		uint64_t rval = h_cede();
> > +
> > +		if (rval != H_SUCCESS)
> > +			pass = false;
> > +		sleep(5000);
> > +	}
> > +
> > +	report("H_CEDE TM", pass);
> > +}
> > +
> > +struct {
> > +	const char *name;
> > +	void (*func)(int argc, char **argv);
> > +} hctests[] = {
> > +	{ "h_cede_tm", test_h_cede_tm },
> > +	{ NULL, NULL }
> > +};
> > +
> > +int main(int argc, char **argv)
> > +{
> > +	bool all = false;
> > +	int i;
> > +
> > +	report_prefix_push("tm");
> > +
> > +	all = (argc = 1 || (argc = 2 && !strcmp(argv[1],
> > "all")));
> > +
> > +	for (i = 0; hctests[i].name != NULL; i++) {
> > +		if (all || strcmp(argv[1], hctests[i].name) = 0)
> > {
> > +			report_prefix_push(hctests[i].name);
> > +			hctests[i].func(argc, argv);
> > +			report_prefix_pop();
> > +		}
> > +	}
> > +
> > +	return report_summary();
> > +}
>  Thomas
> 
Thanks for the review, I agree with pretty much all of your comments
and will incorporate them into the next review.