Re: [PATCH v6 18/19] x86: Add support for generic vDSO

Vincenzo Frascino
2019-06-04T12:13:26Z

Hi Michael,

On 30/05/2019 16:41, Michael Kelley wrote:
> From: Vincenzo Frascino <vincenzo.frascino@arm.com> On Thursday, May 30, 2019 7:16 AM
>>
>> The x86 vDSO library requires some adaptations to take advantage of the
>> newly introduced generic vDSO library.
>>
>> Introduce the following changes:
>> - Modification of vdso.c to be compliant with the common vdso datapage
>> - Use of lib/vdso for gettimeofday
>>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>>
>>
>> diff --git a/arch/x86/include/asm/mshyperv-tsc.h b/arch/x86/include/asm/mshyperv-tsc.h
>> new file mode 100644
>> index 000000000000..99c98ccea0bf
>> --- /dev/null
>> +++ b/arch/x86/include/asm/mshyperv-tsc.h
>> @@ -0,0 +1,76 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef _ASM_X86_MSHYPER_TSCPAGE_H
>> +#define _ASM_X86_MSHYPER_TSCPAGE_H
>> +
>> +#include <asm/hyperv-tlfs.h>
>> +
>> +#ifdef CONFIG_HYPERV_TSCPAGE
>> +struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
>> +static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
>> + u64 *cur_tsc)
>> +{
>> + u64 scale, offset;
>> + u32 sequence;
>> +
>> + /*
>> + * The protocol for reading Hyper-V TSC page is specified in Hypervisor
>> + * Top-Level Functional Specification ver. 3.0 and above. To get the
>> + * reference time we must do the following:
>> + * - READ ReferenceTscSequence
>> + * A special '0' value indicates the time source is unreliable and we
>> + * need to use something else. The currently published specification
>> + * versions (up to 4.0b) contain a mistake and wrongly claim '-1'
>> + * instead of '0' as the special value, see commit c35b82ef0294.
>> + * - ReferenceTime =
>> + * ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
>> + * - READ ReferenceTscSequence again. In case its value has changed
>> + * since our first reading we need to discard ReferenceTime and repeat
>> + * the whole sequence as the hypervisor was updating the page in
>> + * between.
>> + */
>> + do {
>> + sequence = READ_ONCE(tsc_pg->tsc_sequence);
>> + if (!sequence)
>> + return U64_MAX;
>> + /*
>> + * Make sure we read sequence before we read other values from
>> + * TSC page.
>> + */
>> + smp_rmb();
>> +
>> + scale = READ_ONCE(tsc_pg->tsc_scale);
>> + offset = READ_ONCE(tsc_pg->tsc_offset);
>> + *cur_tsc = rdtsc_ordered();
>> +
>> + /*
>> + * Make sure we read sequence after we read all other values
>> + * from TSC page.
>> + */
>> + smp_rmb();
>> +
>> + } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
>> +
>> + return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
>> +}
>> +
>> +static inline u64 hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
>> +{
>> + u64 cur_tsc;
>> +
>> + return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
>> +}
>> +
>> +#else
>> +static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
>> +{
>> + return NULL;
>> +}
>> +
>> +static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
>> + u64 *cur_tsc)
>> +{
>> + BUG();
>> + return U64_MAX;
>> +}
>> +#endif
>> +#endif
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index cc60e617931c..db095a992f3e 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -7,6 +7,7 @@
>> #include <linux/nmi.h>
>> #include <asm/io.h>
>> #include <asm/hyperv-tlfs.h>
>> +#include <asm/mshyperv-tsc.h>
>> #include <asm/nospec-branch.h>
>>
>> #define VP_INVAL U32_MAX
>> @@ -387,73 +388,4 @@ static inline int hyperv_flush_guest_mapping_range(u64 as,
>> }
>> #endif /* CONFIG_HYPERV */
>>
>> -#ifdef CONFIG_HYPERV_TSCPAGE
>> -struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
>> -static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
>> - u64 *cur_tsc)
>> -{
>> - u64 scale, offset;
>> - u32 sequence;
>> -
>> - /*
>> - * The protocol for reading Hyper-V TSC page is specified in Hypervisor
>> - * Top-Level Functional Specification ver. 3.0 and above. To get the
>> - * reference time we must do the following:
>> - * - READ ReferenceTscSequence
>> - * A special '0' value indicates the time source is unreliable and we
>> - * need to use something else. The currently published specification
>> - * versions (up to 4.0b) contain a mistake and wrongly claim '-1'
>> - * instead of '0' as the special value, see commit c35b82ef0294.
>> - * - ReferenceTime =
>> - * ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
>> - * - READ ReferenceTscSequence again. In case its value has changed
>> - * since our first reading we need to discard ReferenceTime and repeat
>> - * the whole sequence as the hypervisor was updating the page in
>> - * between.
>> - */
>> - do {
>> - sequence = READ_ONCE(tsc_pg->tsc_sequence);
>> - if (!sequence)
>> - return U64_MAX;
>> - /*
>> - * Make sure we read sequence before we read other values from
>> - * TSC page.
>> - */
>> - smp_rmb();
>> -
>> - scale = READ_ONCE(tsc_pg->tsc_scale);
>> - offset = READ_ONCE(tsc_pg->tsc_offset);
>> - *cur_tsc = rdtsc_ordered();
>> -
>> - /*
>> - * Make sure we read sequence after we read all other values
>> - * from TSC page.
>> - */
>> - smp_rmb();
>> -
>> - } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
>> -
>> - return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
>> -}
>> -
>> -static inline u64 hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
>> -{
>> - u64 cur_tsc;
>> -
>> - return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
>> -}
>> -
>> -#else
>> -static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
>> -{
>> - return NULL;
>> -}
>> -
>> -static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
>> - u64 *cur_tsc)
>> -{
>> - BUG();
>> - return U64_MAX;
>> -}
>> -#endif
>> #endif
>
> Vincenzo -- these changes for Hyper-V are a subset of a larger patch set
> I have that moves all of the Hyper-V clock/timer code into a separate
> clocksource driver in drivers/clocksource, with an include file in
> includes/clocksource. That new include file should be able to work
> instead of your new mshyperv-tsc.h. It also has the benefit of being
> ISA neutral, so it will work with my in-progress patch set to support
> Linux on Hyper-V on ARM64. See https://lkml.org/lkml/2019/5/27/231
> for the new clocksource driver patch set.
>

Thank you for pointing this out, I will rebase my changes on your patches.

> Michael
>

--
Regards,
Vincenzo