linux-kernel - Re: [PATCH v3 3/3] s390: convert to GENERIC

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Date:   Wed, 05 Aug 2020 08:33:31 +0200
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        hca@...ux.ibm.com
Subject: Re: [PATCH v3 3/3] s390: convert to GENERIC_VDSO

Hi Thomas,

Thomas Gleixner <tglx@...utronix.de> writes:

> Sven Schnelle <svens@...ux.ibm.com> writes:
>> --- /dev/null
>> +++ b/arch/s390/include/asm/vdso/data.h
>> @@ -0,0 +1,13 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef __S390_ASM_VDSO_DATA_H
>> +#define __S390_ASM_VDSO_DATA_H
>> +
>> +#include <linux/types.h>
>> +#include <vdso/datapage.h>
>
> I don't think this header needs vdso/datapage.h

Agreed.

>> +struct arch_vdso_data {
>> +	__u64 tod_steering_delta;
>> +	__u64 tod_steering_end;
>> +};
>> +
>> +#endif /* __S390_ASM_VDSO_DATA_H */
>
>> --- /dev/null
>> +++ b/arch/s390/include/asm/vdso/gettimeofday.h
>
>> +static inline u64 __arch_get_hw_counter(s32 clock_mode)
>> +{
>> +	const struct vdso_data *vdso = __arch_get_vdso_data();
>
> If you go and implement time namespace support for VDSO then this
> becomes a problem. See do_hres_timens().
>
> As we did not expect that this function needs vdso_data we should just
> add a vdso_data pointer argument to __arch_get_hw_counter(). And while
> looking at it you're not the first one. MIPS already uses it and because
> it does not support time namespaces so far nobody noticed yet.
>
> That's fine for all others because the compiler will optimize it
> out when it's unused. If the compiler fails to do so, then this is the
> least of our worries :)
>
> As there is no new VDSO conversion pending in next, I can just queue
> that (see below) along with #1 and #2 of this series and send it to
> Linus by end of the week.

Fine with me.

>> +	u64 adj, now;
>> +
>> +	now = get_tod_clock();
>> +	adj = vdso->arch.tod_steering_end - now;
>> +	if (unlikely((s64) adj > 0))
>> +		now += (vdso->arch.tod_steering_delta < 0) ? (adj >> 15) : -(adj >> 15);
>> +	return now;
>> +}
>
>
>> --- /dev/null
>> +++ b/arch/s390/include/asm/vdso/processor.h
>> @@ -0,0 +1,5 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +#ifndef __ASM_VDSO_PROCESSOR_H
>> +#define __ASM_VDSO_PROCESSOR_H
>> +
>> +#endif /* __ASM_VDSO_PROCESSOR_H */
>
> The idea of this file was to provide cpu_relax() self contained without
> pulling in tons of other things from asm/processor.h.

Thanks, i'll add that.

>> diff --git a/arch/s390/include/asm/vdso/vdso.h b/arch/s390/include/asm/vdso/vdso.h
>> new file mode 100644
>> index 000000000000..e69de29bb2d1
>> diff --git a/arch/s390/include/asm/vdso/vsyscall.h b/arch/s390/include/asm/vdso/vsyscall.h
>> new file mode 100644
>> index 000000000000..6c67c08cefdd
>> --- /dev/null
>> +++ b/arch/s390/include/asm/vdso/vsyscall.h
>> @@ -0,0 +1,26 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef __ASM_VDSO_VSYSCALL_H
>> +#define __ASM_VDSO_VSYSCALL_H
>> +
>> +#ifndef __ASSEMBLY__
>> +
>> +#include <linux/hrtimer.h>
>> +#include <linux/timekeeper_internal.h>
>
> I know you copied that from x86 or some other architecture, but thinking
> about the above these two includes are not required for building VDSO
> itself. Only the kernel update side needs them and they are included
> already there. I'm going to remove them from x86 as well.

Thanks, i removed them from my patch.

>> @@ -443,9 +396,8 @@ static void clock_sync_global(unsigned long long delta)
>>  		panic("TOD clock sync offset %lli is too large to drift\n",
>>  		      tod_steering_delta);
>>  	tod_steering_end = now + (abs(tod_steering_delta) << 15);
>> -	vdso_data->ts_dir = (tod_steering_delta < 0) ? 0 : 1;
>> -	vdso_data->ts_end = tod_steering_end;
>> -	vdso_data->tb_update_count++;
>> +	vdso_data->arch.tod_steering_end = tod_steering_end;
>
> Leftover from the previous version. Should be arch_data.tod....

Oops, indeed.

> Heiko, do you consider this 5.9 material or am I right to assume that
> this targets 5.10?

I talked to Heiko yesterday and we agreed that it's to late for 5.9, so
we target 5.10.

Thanks,
Sven