x86/vdso: Add clock_getres() entry point

The generic vDSO library provides an implementation of clock_getres()
that can be leveraged by each architecture.

Add the clock_getres() VDSO entry point on x86.

[ tglx: Massaged changelog and cleaned up the function signature formatting ]

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mips@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Mark Salyzyn <salyzyn@android.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Huw Davies <huw@codeweavers.com>
Cc: Shijith Thotton <sthotton@marvell.com>
Cc: Andre Przywara <andre.przywara@arm.com>
Link: https://lkml.kernel.org/r/20190621095252.32307-24-vincenzo.frascino@arm.com

arch/x86/entry/vdso/vclock_gettime.c

@@ -36,6 +36,7 @@ time_t time(time_t *t)	__attribute__((weak, alias("__vdso_time")));
 #if defined(CONFIG_X86_64) && !defined(BUILD_VDSO32_64)
 /* both 64-bit and x32 use these */
 extern int __vdso_clock_gettime(clockid_t clock, struct __kernel_timespec *ts);
+extern int __vdso_clock_getres(clockid_t clock, struct __kernel_timespec *res);
 
 int __vdso_clock_gettime(clockid_t clock, struct __kernel_timespec *ts)
 {
@@ -45,9 +46,18 @@ int __vdso_clock_gettime(clockid_t clock, struct __kernel_timespec *ts)
 int clock_gettime(clockid_t, struct __kernel_timespec *)
 	__attribute__((weak, alias("__vdso_clock_gettime")));
 
+int __vdso_clock_getres(clockid_t clock,
+			struct __kernel_timespec *res)
+{
+	return __cvdso_clock_getres(clock, res);
+}
+int clock_getres(clockid_t, struct __kernel_timespec *)
+	__attribute__((weak, alias("__vdso_clock_getres")));
+
 #else
 /* i386 only */
 extern int __vdso_clock_gettime(clockid_t clock, struct old_timespec32 *ts);
+extern int __vdso_clock_getres(clockid_t clock, struct old_timespec32 *res);
 
 int __vdso_clock_gettime(clockid_t clock, struct old_timespec32 *ts)
 {
@@ -57,4 +67,11 @@ int __vdso_clock_gettime(clockid_t clock, struct old_timespec32 *ts)
 int clock_gettime(clockid_t, struct old_timespec32 *)
 	__attribute__((weak, alias("__vdso_clock_gettime")));
 
+int __vdso_clock_getres(clockid_t clock, struct old_timespec32 *res)
+{
+	return __cvdso_clock_getres_time32(clock, res);
+}
+
+int clock_getres(clockid_t, struct old_timespec32 *)
+	__attribute__((weak, alias("__vdso_clock_getres")));
 #endif

arch/x86/entry/vdso/vdso.lds.S

@@ -25,6 +25,8 @@ VERSION {
 		__vdso_getcpu;
 		time;
 		__vdso_time;
+		clock_getres;
+		__vdso_clock_getres;
 	local: *;
 	};
 }

arch/x86/entry/vdso/vdso32/vdso32.lds.S

@@ -26,6 +26,7 @@ VERSION
 		__vdso_clock_gettime;
 		__vdso_gettimeofday;
 		__vdso_time;
+		__vdso_clock_getres;
 	};
 
 	LINUX_2.5 {

arch/x86/include/asm/vdso/gettimeofday.h

@@ -24,6 +24,8 @@
 
 #define VDSO_HAS_TIME 1
 
+#define VDSO_HAS_CLOCK_GETRES 1
+
 #ifdef CONFIG_PARAVIRT_CLOCK
 extern u8 pvclock_page[PAGE_SIZE]
 	__attribute__((visibility("hidden")));
@@ -60,6 +62,18 @@ long gettimeofday_fallback(struct __kernel_old_timeval *_tv,
 	return ret;
 }
 
+static __always_inline
+long clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
+{
+	long ret;
+
+	asm ("syscall" : "=a" (ret), "=m" (*_ts) :
+	     "0" (__NR_clock_getres), "D" (_clkid), "S" (_ts) :
+	     "rcx", "r11");
+
+	return ret;
+}
+
 #else
 
 static __always_inline
@@ -97,6 +111,23 @@ long gettimeofday_fallback(struct __kernel_old_timeval *_tv,
 	return ret;
 }
 
+static __always_inline long
+clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
+{
+	long ret;
+
+	asm (
+		"mov %%ebx, %%edx \n"
+		"mov %[clock], %%ebx \n"
+		"call __kernel_vsyscall \n"
+		"mov %%edx, %%ebx \n"
+		: "=a" (ret), "=m" (*_ts)
+		: "0" (__NR_clock_getres_time64), [clock] "g" (_clkid), "c" (_ts)
+		: "edx");
+
+	return ret;
+}
+
 #endif
 
 #ifdef CONFIG_PARAVIRT_CLOCK