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x86, paravirt: Enable pvclock flags in vcpu_time_info structure

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This patch removes one padding byte and transform it into a flags
field. New versions of guests using pvclock will query these flags
upon each read.

Flags, however, will only be interpreted when the guest decides to.
It uses the pvclock_valid_flags function to signal that a specific
set of flags should be taken into consideration. Which flags are valid
are usually devised via HV negotiation.

Signed-off-by: Glauber Costa <glommer@redhat.com>
CC: Jeremy Fitzhardinge <jeremy@goop.org>
Acked-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Glauber Costa
2010-05-11 12:17:39 -04:00
committed by Avi Kivity
parent b69e8caef5
commit 424c32f1aa
3 changed files with 12 additions and 1 deletions
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9
arch/x86/kernel/pvclock.c
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@@ -31,8 +31,16 @@ struct pvclock_shadow_time {
u32 tsc_to_nsec_mul;
int tsc_shift;
u32 version;
u8 flags;
};
static u8 valid_flags __read_mostly = 0;
void pvclock_set_flags(u8 flags)
{
valid_flags = flags;
}
/*
* Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
* yielding a 64-bit result.
@@ -91,6 +99,7 @@ static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
dst->system_timestamp = src->system_time;
dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
dst->tsc_shift = src->tsc_shift;
dst->flags = src->flags;
rmb(); /* test version after fetching data */
} while ((src->version & 1) || (dst->version != src->version));