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From: Vincenzo Frascino <vincenzo.frascino@arm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Will Deacon <will.deacon@arm.com>,
	Russell King <linux@armlinux.org.uk>,
	Ralf Baechle <ralf@linux-mips.org>,
	Mark Salyzyn <salyzyn@android.com>,
	Paul Burton <paul.burton@mips.com>,
	Peter Collingbourne <pcc@google.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 06/28] kernel: Define gettimeofday vdso common code
Date: Tue, 11 Dec 2018 13:54:07 +0000
Message-ID: <97be4423-fb05-69a5-cd01-245e0ff29479@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1811292230430.1657@nanos.tec.linutronix.de>

On 29/11/2018 22:11, Thomas Gleixner wrote:
> Vinzenco,
> 
> On Thu, 29 Nov 2018, Vincenzo Frascino wrote:

[...]

>> +/*
>> + * Returns the clock delta, in nanoseconds left-shifted by the clock
>> + * shift.
>> + */
>> +static __always_inline notrace u64 get_clock_shifted_nsec(u64 cycle_last,
>> +							  u64 mult,
>> +							  u64 mask)
>> +{
>> +	u64 res;
>> +
>> +	/* Read the virtual counter. */
> 
> Virtual counter? No. That's again an ARM thingy. This needs to be done in
> architecture code.
>

I agree, the name choice is unfortunate here. And I should have removed the
comment as well. What this function does is getting the hardware counter, which
seems not ARM specific.

>> +/*
>> + * This hook allows the architecture to validate the arguments
>> + * passed to the library.
>> + */
>> +#ifndef __HAVE_VDSO_ARCH_VALIDATE_ARG
>> +#define __arch_valid_arg(x)	true
>> +#endif
> 
> Why would you need that? There is really no point in adding architecture
> hooks.
>

It is for the bogus. BTW I agree with your comment below. Will remove it in v3.

>> +static notrace int __cvdso_clock_gettime(clockid_t clock,
>> +					 struct __vdso_timespec *ts)
>> +{
>> +	const struct vdso_data *vd = __arch_get_vdso_data();
>> +
>> +	if (!__arch_valid_arg(ts))
> 
> Especially not for a timespec pointer. It's a user space supplied pointer
> and what do you want to validate there? If it's bogus, access will fault,
> end of story.
>>> +		return -EFAULT;
>> +
>> +	switch (clock) {
>> +	case CLOCK_REALTIME:
>> +		if (do_realtime(vd, ts))
>> +			goto fallback;
>> +		break;
>> +	case CLOCK_TAI:
>> +		if (do_tai(vd, ts))
>> +			goto fallback;
>> +		break;
>> +	case CLOCK_MONOTONIC:
>> +		if (do_monotonic(vd, ts))
>> +			goto fallback;
>> +		break;
>> +	case CLOCK_MONOTONIC_RAW:
>> +		if (do_monotonic_raw(vd, ts))
>> +			goto fallback;
>> +		break;
>> +	case CLOCK_BOOTTIME:
>> +		if (do_boottime(vd, ts))
>> +			goto fallback;
>> +		break;
>> +	case CLOCK_REALTIME_COARSE:
>> +		do_realtime_coarse(vd, ts);
>> +		break;
>> +	case CLOCK_MONOTONIC_COARSE:
>> +		do_monotonic_coarse(vd, ts);
>> +		break;
> 
> See the x86 implementation. It avoids the switch case. The reason why you
> want to avoid it is that the compiler will turn that thing above into a
> call table, using an indirect branch and then requiring retpoline.
>

Thanks for providing the rationale here. Going forward I will generalize that
implementation and make sure it works on all the architectures.

[...]

>> +static notrace int __cvdso_clock_getres(clockid_t clock_id,
>> +					struct __vdso_timespec *res)
>> +{
>> +	u64 ns;
>> +
>> +	if (!__arch_valid_arg(res))
>> +		return -EFAULT;
>> +
>> +	if (clock_id == CLOCK_REALTIME ||
>> +	    clock_id == CLOCK_TAI ||
>> +	    clock_id == CLOCK_BOOTTIME ||
>> +	    clock_id == CLOCK_MONOTONIC ||
>> +	    clock_id == CLOCK_MONOTONIC_RAW)
>> +		ns = MONOTONIC_RES_NSEC;
> 
> This is wrong. You cannot unconditionally set that. See what the syscall
> based version does. You always need to verify that the syscall version and
> the vdso version return the same information and not something randomly
> different.
>

Agreed, I will fix it in v3.

> Thanks,
> 
> 	tglx
> 

-- 
Regards,
Vincenzo

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  parent reply index

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-29 17:05 [PATCH v2 00/28] Unify vDSOs across more architectures Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 01/28] kernel: Standardize vdso_datapage Vincenzo Frascino
2018-11-29 22:39   ` Thomas Gleixner
2018-12-11 13:22     ` Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 02/28] kernel: Add Monotonic boot time support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 03/28] kernel: Add International Atomic Time support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 04/28] kernel: Add masks support for Raw and NTP time Vincenzo Frascino
2018-11-29 22:41   ` Thomas Gleixner
2018-12-11 13:24     ` Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 05/28] kernel: Add clock_mode support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 06/28] kernel: Define gettimeofday vdso common code Vincenzo Frascino
2018-11-29 20:42   ` Arnd Bergmann
2018-12-11 13:39     ` Vincenzo Frascino
2018-12-11 21:41       ` Arnd Bergmann
2018-12-13  9:46         ` Vincenzo Frascino
2018-11-29 22:11   ` Thomas Gleixner
2018-11-30 14:29     ` Arnd Bergmann
2018-12-11 14:02       ` Vincenzo Frascino
2018-12-07 17:53     ` Will Deacon
2019-02-08 17:35       ` Will Deacon
2019-02-08 19:28         ` Thomas Gleixner
2019-02-08 19:30           ` Thomas Gleixner
2019-02-13 17:04             ` Will Deacon
2019-02-13 19:35               ` Thomas Gleixner
2019-02-13 17:05           ` Will Deacon
2018-12-11 13:54     ` Vincenzo Frascino [this message]
2018-11-29 17:05 ` [PATCH v2 07/28] arm64: Build vDSO with -ffixed-x18 Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 08/28] arm64: Substitute gettimeofday with C implementation Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 09/28] arm64: compat: Alloc separate pages for vectors and sigpage Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 10/28] arm64: compat: Split kuser32 Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 11/28] arm64: compat: Refactor aarch32_alloc_vdso_pages() Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 12/28] arm64: compat: Add KUSER_HELPERS config option Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 13/28] arm64: compat: Add missing syscall numbers Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 14/28] arm64: compat: Expose signal related structures Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 15/28] arm64: compat: Generate asm offsets for signals Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 16/28] lib: vdso: Add compat support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 17/28] arm64: compat: Add vDSO Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 18/28] arm64: Refactor vDSO code Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 19/28] arm64: compat: vDSO setup for compat layer Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 20/28] arm64: elf: vDSO code page discovery Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 21/28] arm64: compat: Get sigreturn trampolines from vDSO Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 22/28] arm64: Add vDSO compat support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 23/28] arm64: Enable compat vDSO support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 24/28] arm: Add support for generic vDSO Vincenzo Frascino
2018-12-10 22:13   ` Mark Salyzyn
2018-12-11 14:15     ` Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 25/28] mips: Introduce vdso_direct Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 26/28] clock: csrc-4k: Add support for vdso_direct Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 27/28] clock: gic-timer: " Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 28/28] mips: Add support for generic vDSO Vincenzo Frascino

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