Re: [PATCH v2 2/5] powerpc: Fix vDSO clock_getres()

[Christophe Leroy]

Le 16/04/2019 à 18:14, Vincenzo Frascino a écrit :

clock_getres in the vDSO library has to preserve the same behaviour
of posix_get_hrtimer_res().

In particular, posix_get_hrtimer_res() does:
     sec = 0;
     ns = hrtimer_resolution;
and hrtimer_resolution depends on the enablement of the high
resolution timers that can happen either at compile or at run time.

Fix the powerpc vdso implementation of clock_getres keeping a copy of
hrtimer_resolution in vdso data and using that directly.

Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Cc: Paul Mackerras <pau...@samba.org>
Cc: Michael Ellerman <m...@ellerman.id.au>
Signed-off-by: Vincenzo Frascino <vincenzo.frasc...@arm.com>

Reviewed-by: Christophe Leroy <christophe.le...@c-s.fr>

---
  arch/powerpc/include/asm/vdso_datapage.h  | 2 ++
  arch/powerpc/kernel/asm-offsets.c         | 2 +-
  arch/powerpc/kernel/time.c                | 1 +
  arch/powerpc/kernel/vdso32/gettimeofday.S | 7 +++++--
  arch/powerpc/kernel/vdso64/gettimeofday.S | 7 +++++--
  5 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/vdso_datapage.h 
b/arch/powerpc/include/asm/vdso_datapage.h
index bbc06bd72b1f..4333b9a473dc 100644
--- a/arch/powerpc/include/asm/vdso_datapage.h
+++ b/arch/powerpc/include/asm/vdso_datapage.h
@@ -86,6 +86,7 @@ struct vdso_data {
        __s32 wtom_clock_nsec;                  /* Wall to monotonic clock nsec 
*/
        __s64 wtom_clock_sec;                   /* Wall to monotonic clock sec 
*/
        struct timespec stamp_xtime;            /* xtime as at tb_orig_stamp */
+       __u32 hrtimer_res;                      /* hrtimer resolution */
        __u32 syscall_map_64[SYSCALL_MAP_SIZE]; /* map of syscalls  */
        __u32 syscall_map_32[SYSCALL_MAP_SIZE]; /* map of syscalls */
  };
@@ -107,6 +108,7 @@ struct vdso_data {
        __s32 wtom_clock_nsec;
        struct timespec stamp_xtime;    /* xtime as at tb_orig_stamp */
        __u32 stamp_sec_fraction;       /* fractional seconds of stamp_xtime */
+       __u32 hrtimer_res;              /* hrtimer resolution */
        __u32 syscall_map_32[SYSCALL_MAP_SIZE]; /* map of syscalls */
        __u32 dcache_block_size;        /* L1 d-cache block size     */
        __u32 icache_block_size;        /* L1 i-cache block size     */
diff --git a/arch/powerpc/kernel/asm-offsets.c 
b/arch/powerpc/kernel/asm-offsets.c
index 86a61e5f8285..52e4b98a8492 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -383,6 +383,7 @@ int main(void)
        OFFSET(WTOM_CLOCK_NSEC, vdso_data, wtom_clock_nsec);
        OFFSET(STAMP_XTIME, vdso_data, stamp_xtime);
        OFFSET(STAMP_SEC_FRAC, vdso_data, stamp_sec_fraction);
+       OFFSET(CLOCK_REALTIME_RES, vdso_data, hrtimer_res);
        OFFSET(CFG_ICACHE_BLOCKSZ, vdso_data, icache_block_size);
        OFFSET(CFG_DCACHE_BLOCKSZ, vdso_data, dcache_block_size);
        OFFSET(CFG_ICACHE_LOGBLOCKSZ, vdso_data, icache_log_block_size);
@@ -413,7 +414,6 @@ int main(void)
        DEFINE(CLOCK_REALTIME_COARSE, CLOCK_REALTIME_COARSE);
        DEFINE(CLOCK_MONOTONIC_COARSE, CLOCK_MONOTONIC_COARSE);
        DEFINE(NSEC_PER_SEC, NSEC_PER_SEC);
-       DEFINE(CLOCK_REALTIME_RES, MONOTONIC_RES_NSEC);

#ifdef CONFIG_BUG

        DEFINE(BUG_ENTRY_SIZE, sizeof(struct bug_entry));
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index bc0503ef9c9c..62c04a6746d8 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -955,6 +955,7 @@ void update_vsyscall(struct timekeeper *tk)
        vdso_data->wtom_clock_nsec = tk->wall_to_monotonic.tv_nsec;
        vdso_data->stamp_xtime = xt;
        vdso_data->stamp_sec_fraction = frac_sec;
+       vdso_data->hrtimer_res = hrtimer_resolution;
        smp_wmb();
        ++(vdso_data->tb_update_count);
  }
diff --git a/arch/powerpc/kernel/vdso32/gettimeofday.S 
b/arch/powerpc/kernel/vdso32/gettimeofday.S
index afd516b572f8..2b5f9e83c610 100644
--- a/arch/powerpc/kernel/vdso32/gettimeofday.S
+++ b/arch/powerpc/kernel/vdso32/gettimeofday.S
@@ -160,12 +160,15 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
        cror    cr0*4+eq,cr0*4+eq,cr1*4+eq
        bne     cr0,99f

+ mflr r12

+  .cfi_register lr,r12
+       bl      __get_datapage@local
+       lwz     r5,CLOCK_REALTIME_RES(r3)
+       mtlr    r12
        li      r3,0
        cmpli   cr0,r4,0
        crclr   cr0*4+so
        beqlr
-       lis     r5,CLOCK_REALTIME_RES@h
-       ori     r5,r5,CLOCK_REALTIME_RES@l
        stw     r3,TSPC32_TV_SEC(r4)
        stw     r5,TSPC32_TV_NSEC(r4)
        blr
diff --git a/arch/powerpc/kernel/vdso64/gettimeofday.S 
b/arch/powerpc/kernel/vdso64/gettimeofday.S
index 1f324c28705b..f07730f73d5e 100644
--- a/arch/powerpc/kernel/vdso64/gettimeofday.S
+++ b/arch/powerpc/kernel/vdso64/gettimeofday.S
@@ -190,12 +190,15 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
        cror    cr0*4+eq,cr0*4+eq,cr1*4+eq
        bne     cr0,99f

+ mflr r12

+  .cfi_register lr,r12
+       bl      V_LOCAL_FUNC(__get_datapage)
+       lwz     r5,CLOCK_REALTIME_RES(r3)
+       mtlr    r12
        li      r3,0
        cmpldi  cr0,r4,0
        crclr   cr0*4+so
        beqlr
-       lis     r5,CLOCK_REALTIME_RES@h
-       ori     r5,r5,CLOCK_REALTIME_RES@l
        std     r3,TSPC64_TV_SEC(r4)
        std     r5,TSPC64_TV_NSEC(r4)
        blr