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https://github.com/edk2-porting/linux-next.git
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73459e2a1a
This reverts commits0a4e6be9caand80f7fdb1c7. The task migration notifier was originally introduced in order to support the pvclock vsyscall with non-synchronized TSC, but KVM only supports it with synchronized TSC. Hence, on KVM the race condition is only needed due to a bad implementation on the host side, and even then it's so rare that it's mostly theoretical. As far as KVM is concerned it's possible to fix the host, avoiding the additional complexity in the vDSO and the (re)introduction of the task migration notifier. Xen, on the other hand, hasn't yet implemented vsyscall support at all, so we do not care about its plans for non-synchronized TSC. Reported-by: Peter Zijlstra <peterz@infradead.org> Suggested-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
108 lines
2.8 KiB
C
108 lines
2.8 KiB
C
#ifndef _ASM_X86_PVCLOCK_H
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#define _ASM_X86_PVCLOCK_H
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#include <linux/clocksource.h>
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#include <asm/pvclock-abi.h>
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/* some helper functions for xen and kvm pv clock sources */
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cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src);
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u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src);
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void pvclock_set_flags(u8 flags);
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unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src);
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void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
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struct pvclock_vcpu_time_info *vcpu,
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struct timespec *ts);
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void pvclock_resume(void);
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void pvclock_touch_watchdogs(void);
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/*
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* Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
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* yielding a 64-bit result.
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*/
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static inline u64 pvclock_scale_delta(u64 delta, u32 mul_frac, int shift)
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{
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u64 product;
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#ifdef __i386__
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u32 tmp1, tmp2;
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#else
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ulong tmp;
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#endif
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if (shift < 0)
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delta >>= -shift;
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else
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delta <<= shift;
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#ifdef __i386__
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__asm__ (
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"mul %5 ; "
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"mov %4,%%eax ; "
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"mov %%edx,%4 ; "
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"mul %5 ; "
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"xor %5,%5 ; "
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"add %4,%%eax ; "
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"adc %5,%%edx ; "
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: "=A" (product), "=r" (tmp1), "=r" (tmp2)
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: "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
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#elif defined(__x86_64__)
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__asm__ (
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"mulq %[mul_frac] ; shrd $32, %[hi], %[lo]"
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: [lo]"=a"(product),
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[hi]"=d"(tmp)
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: "0"(delta),
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[mul_frac]"rm"((u64)mul_frac));
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#else
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#error implement me!
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#endif
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return product;
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}
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static __always_inline
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u64 pvclock_get_nsec_offset(const struct pvclock_vcpu_time_info *src)
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{
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u64 delta = __native_read_tsc() - src->tsc_timestamp;
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return pvclock_scale_delta(delta, src->tsc_to_system_mul,
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src->tsc_shift);
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}
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static __always_inline
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unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
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cycle_t *cycles, u8 *flags)
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{
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unsigned version;
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cycle_t ret, offset;
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u8 ret_flags;
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version = src->version;
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/* Note: emulated platforms which do not advertise SSE2 support
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* result in kvmclock not using the necessary RDTSC barriers.
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* Without barriers, it is possible that RDTSC instruction reads from
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* the time stamp counter outside rdtsc_barrier protected section
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* below, resulting in violation of monotonicity.
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*/
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rdtsc_barrier();
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offset = pvclock_get_nsec_offset(src);
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ret = src->system_time + offset;
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ret_flags = src->flags;
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rdtsc_barrier();
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*cycles = ret;
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*flags = ret_flags;
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return version;
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}
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struct pvclock_vsyscall_time_info {
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struct pvclock_vcpu_time_info pvti;
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} __attribute__((__aligned__(SMP_CACHE_BYTES)));
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#define PVTI_SIZE sizeof(struct pvclock_vsyscall_time_info)
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#define PVCLOCK_VSYSCALL_NR_PAGES (((NR_CPUS-1)/(PAGE_SIZE/PVTI_SIZE))+1)
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int __init pvclock_init_vsyscall(struct pvclock_vsyscall_time_info *i,
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int size);
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struct pvclock_vcpu_time_info *pvclock_get_vsyscall_time_info(int cpu);
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#endif /* _ASM_X86_PVCLOCK_H */
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