From: Paolo Bonzini <pbonzini@redhat.com>
To: Andy Lutomirski <luto@kernel.org>, x86@kernel.org
Cc: Borislav Petkov <bp@suse.de>,
Peter Zijlstra <peterz@infradead.org>,
John Stultz <john.stultz@linaro.org>,
linux-kernel@vger.kernel.org, Len Brown <lenb@kernel.org>,
Huang Rui <ray.huang@amd.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
kvm@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>,
Radim Krcmar <rkrcmar@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH v3 17/18] x86/kvm/tsc: Drop extra barrier and use rdtsc_ordered in kvmclock
Date: Wed, 17 Jun 2015 09:47:08 +0200 [thread overview]
Message-ID: <558125FC.7010007@redhat.com> (raw)
In-Reply-To: <678981cc4761fb38a793c217c9cac42503cf3719.1434501121.git.luto@kernel.org>
On 17/06/2015 02:36, Andy Lutomirski wrote:
> __pvclock_read_cycles had an unnecessary barrier. Get rid of that
> barrier and clean up the code by just using rdtsc_ordered().
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krcmar <rkrcmar@redhat.com>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Cc: kvm@vger.kernel.org
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
>
> I'm hoping to get an ack for this to go in through -tip. (Arguably
> I'm the maintainer of this code given how it's used, but I should
> still ask for an ack.)
>
> arch/x86/include/asm/pvclock.h | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
Can you send a URL to the rest of the series? I've never even seen v1
or v2 so I have no idea of what this is about.
> diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
> index 6084bce345fc..cf2329ca4812 100644
> --- a/arch/x86/include/asm/pvclock.h
> +++ b/arch/x86/include/asm/pvclock.h
> @@ -62,7 +62,18 @@ static inline u64 pvclock_scale_delta(u64 delta, u32 mul_frac, int shift)
> static __always_inline
> u64 pvclock_get_nsec_offset(const struct pvclock_vcpu_time_info *src)
> {
> - u64 delta = rdtsc() - src->tsc_timestamp;
> + /*
> + * Note: emulated platforms which do not advertise SSE2 support
> + * break rdtsc_ordered, resulting in kvmclock not using the
> + * necessary RDTSC barriers. Without barriers, it is possible
> + * that RDTSC instruction is executed before prior loads,
> + * resulting in violation of monotonicity.
> + *
> + * On an SMP guest without SSE2, it's unclear how anything is
> + * supposed to work correctly, though -- memory fences
> + * (e.g. smp_mb) are important for more than just timing.
> + */
On an SMP guest without SSE2, memory fences are obtained with e.g. "lock
addb $0, (%esp)".
> + u64 delta = rdtsc_ordered() - src->tsc_timestamp;
> return pvclock_scale_delta(delta, src->tsc_to_system_mul,
> src->tsc_shift);
> }
> @@ -76,17 +87,9 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
> u8 ret_flags;
>
> version = src->version;
> - /* Note: emulated platforms which do not advertise SSE2 support
> - * result in kvmclock not using the necessary RDTSC barriers.
> - * Without barriers, it is possible that RDTSC instruction reads from
> - * the time stamp counter outside rdtsc_barrier protected section
> - * below, resulting in violation of monotonicity.
> - */
> - rdtsc_barrier();
> offset = pvclock_get_nsec_offset(src);
> ret = src->system_time + offset;
> ret_flags = src->flags;
> - rdtsc_barrier();
>
> *cycles = ret;
> *flags = ret_flags;
>
next prev parent reply other threads:[~2015-06-17 7:47 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-17 0:35 [PATCH v3 00/18] x86/tsc: Clean up rdtsc helpers Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 01/18] x86/tsc: Inline native_read_tsc and remove __native_read_tsc Andy Lutomirski
2015-06-17 9:26 ` Borislav Petkov
2015-07-06 15:39 ` [tip:x86/asm] x86/asm/tsc: Inline native_read_tsc() and remove __native_read_tsc() tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 02/18] x86/msr/kvm: Remove vget_cycles() Andy Lutomirski
2015-06-17 9:42 ` Borislav Petkov
2015-06-17 13:34 ` Paolo Bonzini
2015-07-06 15:40 ` [tip:x86/asm] x86/asm/tsc, kvm: " tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 03/18] x86/tsc/paravirt: Remove the read_tsc and read_tscp paravirt hooks Andy Lutomirski
2015-06-17 9:56 ` Borislav Petkov
2015-06-17 9:56 ` Borislav Petkov
2015-06-19 15:32 ` Borislav Petkov
2015-06-19 15:32 ` Borislav Petkov
2015-06-19 16:14 ` Andy Lutomirski
2015-06-19 16:14 ` Andy Lutomirski
2015-06-19 17:13 ` Borislav Petkov
2015-06-19 17:13 ` Borislav Petkov
2015-07-06 15:40 ` [tip:x86/asm] x86/asm/tsc, x86/paravirt: Remove read_tsc() and read_tscp() " tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 04/18] x86/tsc: Replace rdtscll with native_read_tsc Andy Lutomirski
2015-06-17 10:03 ` Borislav Petkov
2015-07-06 15:40 ` [tip:x86/asm] x86/asm/tsc: Replace rdtscll() with native_read_tsc () tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 05/18] x86/tsc: Remove the rdtscp and rdtscpll macros Andy Lutomirski
2015-07-06 15:41 ` [tip:x86/asm] x86/asm/tsc: Remove the rdtscp() and rdtscpll() macros tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 06/18] x86/tsc: Use the full 64-bit tsc in tsc_delay Andy Lutomirski
2015-07-06 15:41 ` [tip:x86/asm] x86/asm/tsc: Use the full 64-bit TSC in delay_tsc() tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 07/18] x86/cpu/amd: Use the full 64-bit TSC to detect the 2.6.2 bug Andy Lutomirski
2015-07-06 15:41 ` [tip:x86/asm] x86/asm/tsc, " tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 08/18] baycom_epp: Replace rdtscl() with native_read_tsc() Andy Lutomirski
2015-06-17 0:49 ` Thomas Sailer
2015-06-20 13:54 ` walter harms
2015-06-20 13:54 ` walter harms
2015-06-20 14:14 ` Thomas Gleixner
2015-06-20 14:14 ` Thomas Gleixner
2015-06-20 14:26 ` Andy Lutomirski
2015-06-20 14:26 ` Andy Lutomirski
2015-06-20 16:30 ` Thomas Gleixner
2015-06-20 16:30 ` Thomas Gleixner
2015-07-06 15:42 ` [tip:x86/asm] x86/asm/tsc, drivers/net/hamradio/baycom_epp: " tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 09/18] staging/lirc_serial: Remove TSC-based timing Andy Lutomirski
2015-06-17 0:35 ` Andy Lutomirski
2015-07-06 15:42 ` [tip:x86/asm] x86/asm/tsc, " tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 10/18] input/joystick/analog: Switch from rdtscl() to native_read_tsc() Andy Lutomirski
2015-07-06 15:42 ` [tip:x86/asm] x86/asm/tsc, " tip-bot for Andy Lutomirski
2015-06-17 0:35 ` [PATCH v3 11/18] drivers/input/gameport: Replace rdtscl() with native_read_tsc() Andy Lutomirski
2015-07-06 15:43 ` [tip:x86/asm] x86/asm/tsc, drivers/input/gameport: Replace rdtscl () " tip-bot for Andy Lutomirski
2015-06-17 0:36 ` [PATCH v3 12/18] x86/tsc: Remove rdtscl() Andy Lutomirski
2015-07-06 15:43 ` [tip:x86/asm] x86/asm/tsc: " tip-bot for Andy Lutomirski
2015-06-17 0:36 ` [PATCH v3 13/18] x86/tsc: Rename native_read_tsc() to rdtsc() Andy Lutomirski
2015-06-24 21:38 ` Borislav Petkov
2015-07-06 15:43 ` [tip:x86/asm] x86/asm/tsc: " tip-bot for Andy Lutomirski
2015-06-17 0:36 ` [PATCH v3 14/18] x86: Add rdtsc_ordered() and use it in trivial call sites Andy Lutomirski
2015-07-06 15:44 ` [tip:x86/asm] x86/asm/tsc: " tip-bot for Andy Lutomirski
2015-08-21 7:45 ` [tip:x86/asm] x86/asm/tsc: Add rdtscll() merge helper tip-bot for Ingo Molnar
2015-06-17 0:36 ` [PATCH v3 15/18] x86/tsc: Use rdtsc_ordered() in check_tsc_warp() and drop extra barriers Andy Lutomirski
2015-07-06 15:44 ` [tip:x86/asm] x86/asm/tsc/sync: " tip-bot for Andy Lutomirski
2015-06-17 0:36 ` [PATCH v3 16/18] x86/tsc: In read_tsc, use rdtsc_ordered() instead of get_cycles() Andy Lutomirski
2015-07-06 15:44 ` [tip:x86/asm] x86/asm/tsc: Use rdtsc_ordered() in read_tsc() " tip-bot for Andy Lutomirski
2015-06-17 0:36 ` [PATCH v3 17/18] x86/kvm/tsc: Drop extra barrier and use rdtsc_ordered in kvmclock Andy Lutomirski
2015-06-17 7:47 ` Paolo Bonzini [this message]
2015-06-17 13:31 ` Paolo Bonzini
2015-06-20 21:50 ` Borislav Petkov
2015-06-20 21:50 ` Borislav Petkov
2015-07-06 15:45 ` [tip:x86/asm] x86/asm/tsc, x86/kvm: Drop open-coded barrier and use rdtsc_ordered() " tip-bot for Andy Lutomirski
2015-06-17 0:36 ` [PATCH v3 18/18] x86/tsc: Remove rdtsc_barrier() Andy Lutomirski
2015-07-06 15:45 ` [tip:x86/asm] x86/asm/tsc: " tip-bot for Andy Lutomirski
2015-06-17 11:11 ` [PATCH v3 00/18] x86/tsc: Clean up rdtsc helpers Borislav Petkov
2015-06-17 13:37 ` Paolo Bonzini
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