powerpc: Fix vDSO clock_getres()

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.

Fixes: a7f290da ("[PATCH] powerpc: Merge vdso's and add vdso support to 32 bits kernel")
Cc: stable@vger.kernel.org
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
[chleroy: changed CLOCK_REALTIME_RES to CLOCK_HRTIMER_RES]
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a55eca3a5e85233838c2349783bcb5164dae1d09.1575273217.git.christophe.leroy@c-s.fr

arch/powerpc/include/asm/vdso_datapage.h

@@ -83,6 +83,7 @@ struct vdso_data {
 	__s64 wtom_clock_sec;			/* Wall to monotonic clock sec */
 	__s64 stamp_xtime_sec;			/* xtime secs as at tb_orig_stamp */
 	__s64 stamp_xtime_nsec;			/* xtime nsecs 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 */
 };
@@ -105,6 +106,7 @@ struct vdso_data {
 	__s32 stamp_xtime_sec;		/* xtime seconds as at tb_orig_stamp */
 	__s32 stamp_xtime_nsec;		/* xtime nsecs 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     */

arch/powerpc/kernel/asm-offsets.c

@@ -388,6 +388,7 @@ int main(void)
 	OFFSET(STAMP_XTIME_SEC, vdso_data, stamp_xtime_sec);
 	OFFSET(STAMP_XTIME_NSEC, vdso_data, stamp_xtime_nsec);
 	OFFSET(STAMP_SEC_FRAC, vdso_data, stamp_sec_fraction);
+	OFFSET(CLOCK_HRTIMER_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));

arch/powerpc/kernel/time.c

@@ -960,6 +960,7 @@ void update_vsyscall(struct timekeeper *tk)
 	vdso_data->stamp_xtime_sec = xt.tv_sec;
 	vdso_data->stamp_xtime_nsec = xt.tv_nsec;
 	vdso_data->stamp_sec_fraction = frac_sec;
+	vdso_data->hrtimer_res = hrtimer_resolution;
 	smp_wmb();
 	++(vdso_data->tb_update_count);
 }

arch/powerpc/kernel/vdso32/gettimeofday.S

@@ -154,12 +154,15 @@ 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	/* get data page */
+	lwz	r5, CLOCK_HRTIMER_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

arch/powerpc/kernel/vdso64/gettimeofday.S

@@ -186,12 +186,15 @@ 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_HRTIMER_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