Messages in this thread | | | Date | Fri, 23 Nov 2018 12:03:07 -0800 | From | Guenter Roeck <> | Subject | Re: [PATCH] x86/TSC: Use RDTSCP |
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Hi,
On Mon, Nov 19, 2018 at 07:45:56PM +0100, Borislav Petkov wrote: > From: Borislav Petkov <bp@suse.de> > > Currently, the kernel uses > > [LM]FENCE; RDTSC > > in the timekeeping code, to guarantee monotonicity of time where the > *FENCE is selected based on vendor. > > Replace that sequence with RDTSCP which is faster or on-par and gives > the same guarantees. > > A microbenchmark on Intel shows that the change is on-par. > > On AMD, the change is either on-par with the current LFENCE-prefixed > RDTSC and some are slightly better with RDTSCP. > > The comparison is done with the LFENCE-prefixed RDTSC (and not with the > MFENCE-prefixed one, as one would normally expect) because all modern > AMD families make LFENCE serializing and thus avoid the heavy MFENCE by > effectively enabling X86_FEATURE_LFENCE_RDTSC. > > Co-developed-by: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Borislav Petkov <bp@suse.de> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: John Stultz <john.stultz@linaro.org> > Cc: Thomas Lendacky <Thomas.Lendacky@amd.com> > Cc: x86@kernel.org > --- > arch/x86/include/asm/msr.h | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h > index 91e4cf189914..f00f2b61d326 100644 > --- a/arch/x86/include/asm/msr.h > +++ b/arch/x86/include/asm/msr.h > @@ -217,6 +217,8 @@ static __always_inline unsigned long long rdtsc(void) > */ > static __always_inline unsigned long long rdtsc_ordered(void) > { > + DECLARE_ARGS(val, low, high); > + > /* > * The RDTSC instruction is not ordered relative to memory > * access. The Intel SDM and the AMD APM are both vague on this > @@ -227,9 +229,18 @@ static __always_inline unsigned long long rdtsc_ordered(void) > * ordering guarantees as reading from a global memory location > * that some other imaginary CPU is updating continuously with a > * time stamp. > + * > + * Thus, use the preferred barrier on the respective CPU, aiming for > + * RDTSCP as the default. > */ > - barrier_nospec(); > - return rdtsc(); > + asm volatile(ALTERNATIVE_2("mfence; rdtsc", > + "lfence; rdtsc", X86_FEATURE_LFENCE_RDTSC, > + "rdtscp", X86_FEATURE_RDTSCP) > + : EAX_EDX_RET(val, low, high) > + /* RDTSCP clobbers ECX with MSR_TSC_AUX. */ > + :: "ecx"); > + > + return EAX_EDX_VAL(val, low, high); > } >
This patch results in a crash with certain qemu emulations.
[ 0.756869] hpet0: 3 comparators, 64-bit 100.000000 MHz counter [ 0.762233] invalid opcode: 0000 [#1] PTI [ 0.762435] CPU: 0 PID: 1 Comm: swapper Not tainted 4.20.0-rc3-next-20181123 #2 [ 0.762644] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 [ 0.762832] EIP: read_tsc+0x4/0x10
To reproduce:
make ARCH=i386 defconfig echo "CONFIG_HIGHMEM64G=y" >> .config make ARCH=i386 olddefconfig make -j30 ARCH=i386
qemu-system-i386 \ -kernel arch/x86/boot/bzImage \ -M q35 -cpu pentium3 -no-reboot -m 256 \ -initrd rootfs.cpio \ --append 'earlycon=uart8250,io,0x3f8,9600n8 rdinit=/sbin/init panic=-1 console=ttyS0 console=tty' \ -nographic -monitor none
initrd or root file system doesn't really matter since the code never gets there, but it is available from here: https://github.com/groeck/linux-build-test/blob/master/rootfs/x86/rootfs.cpio.gz The qemu version does not matter either (I tried with 2.5 and 3.0).
Reverting the patch fixes the problem.
Guenter
--- crash log:
... [ 0.756366] HPET: 3 timers in total, 0 timers will be used for per-cpu timer [ 0.756718] hpet0: at MMIO 0xfed00000, IRQs 2, 8, 0 [ 0.756869] hpet0: 3 comparators, 64-bit 100.000000 MHz counter [ 0.762233] invalid opcode: 0000 [#1] PTI [ 0.762435] CPU: 0 PID: 1 Comm: swapper Not tainted 4.20.0-rc3-next-20181123 #2 [ 0.762644] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 [ 0.762832] EIP: read_tsc+0x4/0x10 [ 0.762832] Code: 00 01 00 eb 89 90 55 89 e5 5d c3 90 90 90 90 90 90 90 90 90 90 90 55 a1 44 5a 8b c5 89 e5 5d c3 8d b6 00 00 00 00 55 89 e5 57 <0f> ae f0b [ 0.762832] EAX: c58062c0 EBX: c58062c0 ECX: 00000008 EDX: c4c1f0a0 [ 0.762832] ESI: c58168c0 EDI: 00200086 EBP: cb495ed4 ESP: cb495ed0 [ 0.762832] DS: 007b ES: 007b FS: 0000 GS: 00e0 SS: 0068 EFLAGS: 00200002 [ 0.762832] CR0: 80050033 CR2: 00000000 CR3: 0597a000 CR4: 000006f0 [ 0.762832] Call Trace: [ 0.762832] tk_setup_internals.constprop.10+0x3d/0x260 [ 0.762832] timekeeping_notify+0x56/0xc0 [ 0.762832] __clocksource_select+0xf3/0x150 [ 0.762832] ? boot_override_clock+0x42/0x42 [ 0.762832] clocksource_done_booting+0x2d/0x3b [ 0.762832] do_one_initcall+0x68/0x15e [ 0.762832] ? set_debug_rodata+0xf/0xf [ 0.762832] kernel_init_freeable+0xec/0x18b [ 0.762832] ? rest_init+0x80/0x80 [ 0.762832] kernel_init+0x8/0xf0 [ 0.762832] ret_from_fork+0x2e/0x38 [ 0.762832] Modules linked in: [ 0.762832] ---[ end trace ba4ba4587aec46c9 ]--- [ 0.762832] EIP: read_tsc+0x4/0x10 [ 0.762832] Code: 00 01 00 eb 89 90 55 89 e5 5d c3 90 90 90 90 90 90 90 90 90 90 90 55 a1 44 5a 8b c5 89 e5 5d c3 8d b6 00 00 00 00 55 89 e5 57 <0f> ae f0b [ 0.762832] EAX: c58062c0 EBX: c58062c0 ECX: 00000008 EDX: c4c1f0a0 [ 0.762832] ESI: c58168c0 EDI: 00200086 EBP: cb495ed4 ESP: c597f47c [ 0.762832] DS: 007b ES: 007b FS: 0000 GS: 00e0 SS: 0068 EFLAGS: 00200002 [ 0.762832] CR0: 80050033 CR2: 00000000 CR3: 0597a000 CR4: 000006f0
--- bisect log:
# bad: [8c9733fd9806c71e7f2313a280f98cb3051f93df] Add linux-next specific files for 20181123 # good: [9ff01193a20d391e8dbce4403dd5ef87c7eaaca6] Linux 4.20-rc3 git bisect start 'HEAD' 'v4.20-rc3' # good: [34c2101b4f765edf1b91c2837da9c60fbf9f6912] Merge remote-tracking branch 'spi-nor/spi-nor/next' git bisect good 34c2101b4f765edf1b91c2837da9c60fbf9f6912 # good: [15367a0657fc8027ff3466bf0202bde9f270259b] Merge remote-tracking branch 'kgdb/kgdb-next' git bisect good 15367a0657fc8027ff3466bf0202bde9f270259b # bad: [d29686ab179c34c5dbaac067a9effbeeb6a8073e] Merge remote-tracking branch 'soundwire/next' git bisect bad d29686ab179c34c5dbaac067a9effbeeb6a8073e # bad: [7cd63670817c236ccaf21ffe9d7b4921afeab130] Merge remote-tracking branch 'tip/auto-latest' git bisect bad 7cd63670817c236ccaf21ffe9d7b4921afeab130 # good: [f9c8ebdcb052214954136426990e13a88e45e906] Merge remote-tracking branch 'audit/next' git bisect good f9c8ebdcb052214954136426990e13a88e45e906 # good: [4142a8a10e7673fa71ff4cb5b4693c4dda299f7c] Merge remote-tracking branch 'spi/for-next' git bisect good 4142a8a10e7673fa71ff4cb5b4693c4dda299f7c # good: [fc922a4c7c72131f6c65e4af4e36ff25f3af1485] Merge branch 'x86/cpu' git bisect good fc922a4c7c72131f6c65e4af4e36ff25f3af1485 # good: [906d11c1ff007ad18e2f3477cca04c437ce19c64] Merge branch 'x86/microcode' git bisect good 906d11c1ff007ad18e2f3477cca04c437ce19c64 # good: [d836e1d42739a86738dd92a1b7ab6729b2485cba] Merge branch 'x86/platform' git bisect good d836e1d42739a86738dd92a1b7ab6729b2485cba # bad: [191bba684b7459842e72b52718ec61f8bdbd8499] Merge branch 'x86/timers' git bisect bad 191bba684b7459842e72b52718ec61f8bdbd8499 # good: [f9cc0921aa4edd9bd4dd6943d5e38f69a301e8ee] Merge branch 'x86/pti' git bisect good f9cc0921aa4edd9bd4dd6943d5e38f69a301e8ee # bad: [2e94061096c5c3aa6c3fe3ec2bec176c1f9c1b07] x86/TSC: Use RDTSCP git bisect bad 2e94061096c5c3aa6c3fe3ec2bec176c1f9c1b07 # good: [a786ef152cdcfebc923a67f63c7815806eefcf81] x86/tsc: Make calibration refinement more robust git bisect good a786ef152cdcfebc923a67f63c7815806eefcf81 # first bad commit: [2e94061096c5c3aa6c3fe3ec2bec176c1f9c1b07] x86/TSC: Use RDTSCP
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