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@xxxxxxxxxx>
---
arch/x86/include/asm/pvclock-abi.h | 3 ++-
arch/x86/include/asm/pvclock.h | 1 +
arch/x86/kernel/pvclock.c | 9 +++++++++
3 files changed, 12 insertions(+), 1 deletions(-)
diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
index 6d93508..ec5c41a 100644
--- a/arch/x86/include/asm/pvclock-abi.h
+++ b/arch/x86/include/asm/pvclock-abi.h
@@ -29,7 +29,8 @@ struct pvclock_vcpu_time_info {
u64 system_time;
u32 tsc_to_system_mul;
s8 tsc_shift;
- u8 pad[3];
+ u8 flags;
+ u8 pad[2];
} __attribute__((__packed__)); /* 32 bytes */
struct pvclock_wall_clock {
diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 53235fd..c50823f 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -6,6 +6,7 @@
/* some helper functions for xen and kvm pv clock sources */
cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src);
+void pvclock_valid_flags(u8 flags);
unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src);
void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
struct pvclock_vcpu_time_info *vcpu,
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 03801f2..8f4af7b 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -31,8 +31,16 @@ struct pvclock_shadow_time {
u32 tsc_to_nsec_mul;
int tsc_shift;
u32 version;
+ u8 flags;
};
+static u8 valid_flags = 0;
+
+void pvclock_valid_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));
--
1.6.2.2
--
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