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Commit 4e87173e authored by Glauber de Oliveira Costa's avatar Glauber de Oliveira Costa Committed by Ingo Molnar
Browse files

x86: split get_cycles_sync 



This patch splits get_cycles_sync() into  __get_cycles_sync(),
and the rdtscll part. Paravirt guests cannot issue rdtscl directly,
as it involves a function call in vdso area.

So, using the __get_cycles_sync() base, we introduce vget_cycles_sync,
which then calls the native version of rdtscll. Ideally, however, a guest
should define its own clocksource, together with a vread function

Signed-off-by: default avatarGlauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 16e2011b

arch/x86/kernel/tsc_64.c

+1 −1
Original line number Diff line number Diff line
@@ -306,7 +306,7 @@ static cycle_t read_tsc(void) 


static cycle_t __vsyscall_fn vread_tsc(void)

{

	cycle_t ret = (cycle_t)get_cycles_sync();

	cycle_t ret = (cycle_t)vget_cycles_sync();

	return ret;

}

include/asm-x86/tsc.h

+33 −4
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ static inline cycles_t get_cycles(void) 
}



/* Like get_cycles, but make sure the CPU is synchronized. */

static __always_inline cycles_t get_cycles_sync(void)

static __always_inline cycles_t __get_cycles_sync(void)

{

	unsigned long long ret;

	unsigned eax, edx;
@@ -55,10 +55,39 @@ static __always_inline cycles_t get_cycles_sync(void) 
	 */

	alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,

			  "=a" (eax), "0" (1) : "ebx","ecx","edx","memory");



	return 0;

}



static __always_inline cycles_t get_cycles_sync(void)

{

	unsigned long long ret;

	ret = __get_cycles_sync();

	if (!ret)

		rdtscll(ret);

	return ret;

}



#ifdef CONFIG_PARAVIRT

/*

 * For paravirt guests, some functionalities are executed through function

 * pointers in the various pvops structures.

 * These function pointers exist inside the kernel and can not

 * be accessed by user space. To avoid this, we make a copy of the

 * get_cycles_sync (called in kernel) but force the use of native_read_tsc.

 * Ideally, the guest should set up it's own clock and vread

 */

static __always_inline long long vget_cycles_sync(void)

{

	unsigned long long ret;

	ret = __get_cycles_sync();

	if (!ret)

		ret = native_read_tsc();

	return ret;

}

#else

# define vget_cycles_sync() get_cycles_sync()

#endif



extern void tsc_init(void);

extern void mark_tsc_unstable(char *reason);