Re: [kvm-unit-tests PATCH v8 6/6] s390x: SCLP unit test

[Thomas Huth <thuth@redhat.com>]

On 22/01/2020 11.32, David Hildenbrand wrote:
> On 22.01.20 11:31, Thomas Huth wrote:
>> On 22/01/2020 11.22, David Hildenbrand wrote:
>>> On 22.01.20 11:10, David Hildenbrand wrote:
>>>> On 20.01.20 19:42, Claudio Imbrenda wrote:
>>>>> SCLP unit test. Testing the following:
>>>>>
>>>>> * Correctly ignoring instruction bits that should be ignored
>>>>> * Privileged instruction check
>>>>> * Check for addressing exceptions
>>>>> * Specification exceptions:
>>>>>   - SCCB size less than 8
>>>>>   - SCCB unaligned
>>>>>   - SCCB overlaps prefix or lowcore
>>>>>   - SCCB address higher than 2GB
>>>>> * Return codes for
>>>>>   - Invalid command
>>>>>   - SCCB too short (but at least 8)
>>>>>   - SCCB page boundary violation
>>>>>
>>>>> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
>>>>> Reviewed-by: Thomas Huth <thuth@redhat.com>
>>>>> Acked-by: Janosch Frank <frankja@linux.ibm.com>
>>>>> ---
>>>>>  s390x/Makefile      |   1 +
>>>>>  s390x/sclp.c        | 474 ++++++++++++++++++++++++++++++++++++++++++++
>>>>>  s390x/unittests.cfg |   8 +
>>>>>  3 files changed, 483 insertions(+)
>>>>>  create mode 100644 s390x/sclp.c
>>>>>
>>>>> diff --git a/s390x/Makefile b/s390x/Makefile
>>>>> index 3744372..ddb4b48 100644
>>>>> --- a/s390x/Makefile
>>>>> +++ b/s390x/Makefile
>>>>> @@ -16,6 +16,7 @@ tests += $(TEST_DIR)/diag288.elf
>>>>>  tests += $(TEST_DIR)/stsi.elf
>>>>>  tests += $(TEST_DIR)/skrf.elf
>>>>>  tests += $(TEST_DIR)/smp.elf
>>>>> +tests += $(TEST_DIR)/sclp.elf
>>>>>  tests_binary = $(patsubst %.elf,%.bin,$(tests))
>>>>>  
>>>>>  all: directories test_cases test_cases_binary
>>>>> diff --git a/s390x/sclp.c b/s390x/sclp.c
>>>>> new file mode 100644
>>>>> index 0000000..215347e
>>>>> --- /dev/null
>>>>> +++ b/s390x/sclp.c
>>>>> @@ -0,0 +1,474 @@
>>>>> +/*
>>>>> + * Service Call tests
>>>>> + *
>>>>> + * Copyright (c) 2019 IBM Corp
>>>>> + *
>>>>> + * Authors:
>>>>> + *  Claudio Imbrenda <imbrenda@linux.ibm.com>
>>>>> + *
>>>>> + * This code is free software; you can redistribute it and/or modify it
>>>>> + * under the terms of the GNU General Public License version 2.
>>>>> + */
>>>>> +
>>>>> +#include <libcflat.h>
>>>>> +#include <asm/page.h>
>>>>> +#include <asm/asm-offsets.h>
>>>>> +#include <asm/interrupt.h>
>>>>> +#include <sclp.h>
>>>>> +
>>>>> +#define PGM_NONE	1
>>>>> +#define PGM_BIT_SPEC	(1ULL << PGM_INT_CODE_SPECIFICATION)
>>>>> +#define PGM_BIT_ADDR	(1ULL << PGM_INT_CODE_ADDRESSING)
>>>>> +#define PGM_BIT_PRIV	(1ULL << PGM_INT_CODE_PRIVILEGED_OPERATION)
>>>>> +#define MKPTR(x) ((void *)(uint64_t)(x))
>>>>> +
>>>>> +#define LC_SIZE (2 * PAGE_SIZE)
>>>>> +
>>>>> +static uint8_t pagebuf[LC_SIZE] __attribute__((aligned(LC_SIZE)));	/* scratch pages used for some tests */
>>>>> +static uint8_t prefix_buf[LC_SIZE] __attribute__((aligned(LC_SIZE)));	/* temporary lowcore for test_sccb_prefix */
>>>>> +static uint8_t sccb_template[PAGE_SIZE];				/* SCCB template to be used */
>>>>> +static uint32_t valid_code;						/* valid command code for READ SCP INFO */
>>>>> +static struct lowcore *lc;
>>>>> +
>>>>> +/**
>>>>> + * Perform one service call, handling exceptions and interrupts.
>>>>> + */
>>>>> +static int sclp_service_call_test(unsigned int command, void *sccb)
>>>>> +{
>>>>> +	int cc;
>>>>> +
>>>>> +	sclp_mark_busy();
>>>>> +	sclp_setup_int();
>>>>> +	cc = servc(command, __pa(sccb));
>>>>> +	if (lc->pgm_int_code) {
>>>>> +		sclp_handle_ext();
>>>>> +		return 0;
>>>>> +	}
>>>>> +	if (!cc)
>>>>> +		sclp_wait_busy();
>>>>> +	return cc;
>>>>> +}
>>>>> +
>>>>> +/**
>>>>> + * Perform one test at the given address, optionally using the SCCB template,
>>>>> + * checking for the expected program interrupts and return codes.
>>>>> + *
>>>>> + * The parameter buf_len indicates the number of bytes of the template that
>>>>> + * should be copied to the test address, and should be 0 when the test
>>>>> + * address is invalid, in which case nothing is copied.
>>>>> + *
>>>>> + * The template is used to simplify tests where the same buffer content is
>>>>> + * used many times in a row, at different addresses.
>>>>> + *
>>>>> + * Returns true in case of success or false in case of failure
>>>>> + */
>>>>> +static bool test_one_sccb(uint32_t cmd, uint8_t *addr, uint16_t buf_len, uint64_t exp_pgm, uint16_t exp_rc)
>>>>> +{
>>>>> +	SCCBHeader *h = (SCCBHeader *)addr;
>>>>> +	int res, pgm;
>>>>> +
>>>>> +	/* Copy the template to the test address if needed */
>>>>> +	if (buf_len)
>>>>> +		memcpy(addr, sccb_template, buf_len);
>>>>> +	if (exp_pgm != PGM_NONE)
>>>>> +		expect_pgm_int();
>>>>> +	/* perform the actual call */
>>>>> +	res = sclp_service_call_test(cmd, h);
>>>>> +	if (res) {
>>>>> +		report_info("SCLP not ready (command %#x, address %p, cc %d)", cmd, addr, res);
>>>>> +		return false;
>>>>> +	}
>>>>> +	pgm = clear_pgm_int();
>>>>> +	/* Check if the program exception was one of the expected ones */
>>>>> +	if (!((1ULL << pgm) & exp_pgm)) {
>>>>> +		report_info("First failure at addr %p, buf_len %d, cmd %#x, pgm code %d",
>>>>> +				addr, buf_len, cmd, pgm);
>>>>> +		return false;
>>>>> +	}
>>>>> +	/* Check if the response code is the one expected */
>>>>> +	if (exp_rc && exp_rc != h->response_code) {
>>>>> +		report_info("First failure at addr %p, buf_len %d, cmd %#x, resp code %#x",
>>>>> +				addr, buf_len, cmd, h->response_code);
>>>>> +		return false;
>>>>> +	}
>>>>> +	return true;
>>>>> +}
>>>>> +
>>>>> +/**
>>>>> + * Wrapper for test_one_sccb to be used when the template should not be
>>>>> + * copied and the memory address should not be touched.
>>>>> + */
>>>>> +static bool test_one_ro(uint32_t cmd, uint8_t *addr, uint64_t exp_pgm, uint16_t exp_rc)
>>>>> +{
>>>>> +	return test_one_sccb(cmd, addr, 0, exp_pgm, exp_rc);
>>>>> +}
>>>>> +
>>>>> +/**
>>>>> + * Wrapper for test_one_sccb to set up a simple SCCB template.
>>>>> + *
>>>>> + * The parameter sccb_len indicates the value that will be saved in the SCCB
>>>>> + * length field of the SCCB, buf_len indicates the number of bytes of
>>>>> + * template that need to be copied to the actual test address. In many cases
>>>>> + * it's enough to clear/copy the first 8 bytes of the buffer, while the SCCB
>>>>> + * itself can be larger.
>>>>> + *
>>>>> + * Returns true in case of success or false in case of failure
>>>>> + */
>>>>> +static bool test_one_simple(uint32_t cmd, uint8_t *addr, uint16_t sccb_len,
>>>>> +			uint16_t buf_len, uint64_t exp_pgm, uint16_t exp_rc)
>>>>> +{
>>>>> +	memset(sccb_template, 0, sizeof(sccb_template));
>>>>> +	((SCCBHeader *)sccb_template)->length = sccb_len;
>>>>> +	return test_one_sccb(cmd, addr, buf_len, exp_pgm, exp_rc);
>>>>
>>>> Doing a fresh ./configure + make on RHEL7 gives me
>>>>
>>>> [linux1@rhkvm01 kvm-unit-tests]$ make
>>>> gcc  -std=gnu99 -ffreestanding -I /home/linux1/git/kvm-unit-tests/lib -I /home/linux1/git/kvm-unit-tests/lib/s390x -I lib -O2 -march=zEC12 -fno-delete-null-pointer-checks -g -MMD -MF s390x/.sclp.d -Wall -Wwrite-strings -Wempty-body -Wuninitialized -Wignored-qualifiers -Werror  -fomit-frame-pointer    -Wno-frame-address   -fno-pic    -Wclobbered  -Wunused-but-set-parameter  -Wmissing-parameter-type  -Wold-style-declaration -Woverride-init -Wmissing-prototypes -Wstrict-prototypes   -c -o s390x/sclp.o s390x/sclp.c
>>>> s390x/sclp.c: In function 'test_one_simple':
>>>> s390x/sclp.c:121:2: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
>>>>   ((SCCBHeader *)sccb_template)->length = sccb_len;
>>>>   ^
>>>> s390x/sclp.c: At top level:
>>>> cc1: error: unrecognized command line option "-Wno-frame-address" [-Werror]
>>>> cc1: all warnings being treated as errors
>>>> make: *** [s390x/sclp.o] Error 1
>>>
>>> The following makes it work:
>>>
>>>
>>> diff --git a/s390x/sclp.c b/s390x/sclp.c
>>> index c13fa60..0b8117a 100644
>>> --- a/s390x/sclp.c
>>> +++ b/s390x/sclp.c
>>> @@ -117,8 +117,10 @@ static bool test_one_ro(uint32_t cmd, uint8_t *addr, uint64_t exp_pgm, uint16_t
>>>  static bool test_one_simple(uint32_t cmd, uint8_t *addr, uint16_t sccb_len,
>>>                         uint16_t buf_len, uint64_t exp_pgm, uint16_t exp_rc)
>>>  {
>>> +       SCCBHeader *header = (void *)sccb_template;
>>> +
>>>         memset(sccb_template, 0, sizeof(sccb_template));
>>> -       ((SCCBHeader *)sccb_template)->length = sccb_len;
>>> +       header->length = sccb_len;
>>
>> While that might silence the compiler warning, we still might get
>> aliasing problems here, I think.
>> The right way to solve this problem is to turn sccb_template into a
>> union of the various structs/arrays that you want to use and then access
>> the fields through the union instead ("type-punning through union").
> 
> We do have the exact same thing in lib/s390x/sclp.c already, no?

Maybe we should carefully check that code, too...

> Especially, new compilers don't seem to care?

I've seen horrible bugs due to these aliasing problems in the past -
without compiler warnings showing up! Certain versions of GCC assume
that they can re-order code with pointers that point to types of
different sizes, i.e. in the above example, I think they could assume
that they could re-order the memset() and the header->length = ... line.
I'd feel better if we play safe and use a union here.

 Thomas