[PATCH 2/6] x86/hyper-v: add a function to read both TSC and TSC page value simulateneously

[Vitaly Kuznetsov <vkuznets@redhat.com>]

This is going to be used from KVM code where we need to get both
TSC and TSC page value.

When Hyper-V code is compiled out just return rdtsc(), this will allow us
to avoid ugly ifdefs in non-Hyper-V code.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
RFC -> v1:
- EXPORT_SYMBOL_GPL(hv_get_tsc_page) [kbuild test robot]
- BUG() in !CONFIG_HYPERV_TSCPAGE case [Stephen Hemminger, Paolo Bonzini]
- 'were' -> 'where' [Andrew Jones]
---
 arch/x86/hyperv/hv_init.c       |  1 +
 arch/x86/include/asm/mshyperv.h | 23 +++++++++++++++++++----
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 21f9d53d9f00..1a6c63f721bc 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -37,6 +37,7 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
 {
 	return tsc_pg;
 }
+EXPORT_SYMBOL_GPL(hv_get_tsc_page);
 
 static u64 read_hv_clock_tsc(struct clocksource *arg)
 {
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 5400add2885b..a0b34994f453 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -323,9 +323,10 @@ static inline void hyperv_setup_mmu_ops(void) {}
 
 #ifdef CONFIG_HYPERV_TSCPAGE
 struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
-static inline u64 hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
+static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
+				       u64 *cur_tsc)
 {
-	u64 scale, offset, cur_tsc;
+	u64 scale, offset;
 	u32 sequence;
 
 	/*
@@ -356,7 +357,7 @@ static inline u64 hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
 
 		scale = READ_ONCE(tsc_pg->tsc_scale);
 		offset = READ_ONCE(tsc_pg->tsc_offset);
-		cur_tsc = rdtsc_ordered();
+		*cur_tsc = rdtsc_ordered();
 
 		/*
 		 * Make sure we read sequence after we read all other values
@@ -366,7 +367,14 @@ static inline u64 hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
 
 	} while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
 
-	return mul_u64_u64_shr(cur_tsc, scale, 64) + offset;
+	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
@@ -374,5 +382,12 @@ 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
-- 
2.14.3