Re: [kvm-unit-tests PATCH v1 4/4] s390x: edat test

[Thomas Huth <thuth@redhat.com>]

On 09/02/2021 15.38, Claudio Imbrenda wrote:
> Simple EDAT test.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
>   s390x/Makefile      |   1 +
>   s390x/edat.c        | 238 ++++++++++++++++++++++++++++++++++++++++++++
>   s390x/unittests.cfg |   3 +
>   3 files changed, 242 insertions(+)
>   create mode 100644 s390x/edat.c
> 
> diff --git a/s390x/Makefile b/s390x/Makefile
> index 08d85c9f..fc885150 100644
> --- a/s390x/Makefile
> +++ b/s390x/Makefile
> @@ -20,6 +20,7 @@ tests += $(TEST_DIR)/sclp.elf
>   tests += $(TEST_DIR)/css.elf
>   tests += $(TEST_DIR)/uv-guest.elf
>   tests += $(TEST_DIR)/sie.elf
> +tests += $(TEST_DIR)/edat.elf
>   
>   tests_binary = $(patsubst %.elf,%.bin,$(tests))
>   ifneq ($(HOST_KEY_DOCUMENT),)
> diff --git a/s390x/edat.c b/s390x/edat.c
> new file mode 100644
> index 00000000..504a1501
> --- /dev/null
> +++ b/s390x/edat.c
> @@ -0,0 +1,238 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * EDAT test.
> + *
> + * Copyright (c) 2021 IBM Corp
> + *
> + * Authors:
> + *	Claudio Imbrenda <imbrenda@linux.ibm.com>
> + */
> +#include <libcflat.h>
> +#include <vmalloc.h>
> +#include <asm/facility.h>
> +#include <asm/interrupt.h>
> +#include <mmu.h>
> +#include <asm/pgtable.h>
> +#include <asm-generic/barrier.h>
> +
> +#define TEID_ADDR	PAGE_MASK
> +#define TEID_AI		0x003
> +#define TEID_M		0x004
> +#define TEID_A		0x008
> +#define TEID_FS		0xc00
> +
> +#define LC_SIZE	(2 * PAGE_SIZE)
> +#define VIRT(x)	((void *)((unsigned long)(x) + (unsigned long)mem))
> +
> +static uint8_t prefix_buf[LC_SIZE] __attribute__((aligned(LC_SIZE)));
> +static unsigned int tmp[1024] __attribute__((aligned(PAGE_SIZE)));
> +static void *root, *mem, *m;
> +static struct lowcore *lc;
> +volatile unsigned int *p;
> +
> +/* Expect a program interrupt, and clear the TEID */
> +static void expect_dat_fault(void)
> +{
> +	expect_pgm_int();
> +	lc->trans_exc_id = 0;
> +}
> +
> +/* Check if a protection exception happened for the given address */
> +static bool check_pgm_prot(void *ptr)
> +{
> +	unsigned long teid = lc->trans_exc_id;
> +
> +	if (lc->pgm_int_code != PGM_INT_CODE_PROTECTION)
> +		return 0;

return false.
It's a bool return type.

> +	if (~teid & TEID_M)

I'd maybe rather write this as:

         if (!(teid & TEID_M))

... but it's just a matter of taste.

> +		return 1;

                 return true;

So this is for backward compatiblity with older Z systems that do not have 
the corresponding facility? Should there be a corresponding facility check 
somewhere? Or maybe add at least a comment?

> +	return (~teid & TEID_A) &&
> +		((teid & TEID_ADDR) == ((uint64_t)ptr & PAGE_MASK)) &&
> +		!(teid & TEID_AI);

So you're checking for one specific type of protection exception here only 
... please add an appropriate comment.

> +}
> +
> +static void test_dat(void)
> +{
> +	report_prefix_push("edat off");
> +	/* disable EDAT */
> +	ctl_clear_bit(0, 23);
> +
> +	/* Check some basics */
> +	p[0] = 42;
> +	report(p[0] == 42, "pte, r/w");
> +	p[0] = 0;
> +
> +	protect_page(m, PAGE_ENTRY_P);
> +	expect_dat_fault();
> +	p[0] = 42;
> +	unprotect_page(m, PAGE_ENTRY_P);
> +	report(!p[0] && check_pgm_prot(m), "pte, ro");
> +
> +	/* The FC bit should be ignored because EDAT is off */
> +	p[0] = 42;

I'd suggest to set p[0] = 0 here...

> +	protect_dat_entry(m, SEGMENT_ENTRY_FC, 4);

... and change the value to 42 after enabling the protection ... otherwise 
you don't really test the non-working write protection here, do you?

> +	report(p[0] == 42, "pmd, fc=1, r/w");
> +	unprotect_dat_entry(m, SEGMENT_ENTRY_FC, 4);
> +	p[0] = 0;
> +
> +	/* Segment protection should work even with EDAT off */
> +	protect_dat_entry(m, SEGMENT_ENTRY_P, 4);
> +	expect_dat_fault();
> +	p[0] = 42;
> +	report(!p[0] && check_pgm_prot(m), "pmd, ro");
> +	unprotect_dat_entry(m, SEGMENT_ENTRY_P, 4);
> +
> +	/* The FC bit should be ignored because EDAT is off*/

Set p[0] to 0 again before enabling the protection? Or maybe use a different 
value than 42 below...?

> +	protect_dat_entry(m, REGION3_ENTRY_FC, 3);
> +	p[0] = 42;
> +	report(p[0] == 42, "pud, fc=1, r/w");
> +	unprotect_dat_entry(m, REGION3_ENTRY_FC, 3);
> +	p[0] = 0;
> +
> +	/* Region1/2/3 protection should not work, because EDAT is off */
> +	protect_dat_entry(m, REGION_ENTRY_P, 3);
> +	p[0] = 42;
> +	report(p[0] == 42, "pud, ro");
> +	unprotect_dat_entry(m, REGION_ENTRY_P, 3);
> +	p[0] = 0;
> +
> +	protect_dat_entry(m, REGION_ENTRY_P, 2);
> +	p[0] = 42;
> +	report(p[0] == 42, "p4d, ro");
> +	unprotect_dat_entry(m, REGION_ENTRY_P, 2);
> +	p[0] = 0;
> +
> +	protect_dat_entry(m, REGION_ENTRY_P, 1);
> +	p[0] = 42;
> +	report(p[0] == 42, "pgd, ro");
> +	unprotect_dat_entry(m, REGION_ENTRY_P, 1);
> +	p[0] = 0;
> +
> +	report_prefix_pop();
> +}

  Thomas