[PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method

Vitaly Kuznetsov
2017-02-09T14:10:52Z

Hyper-V TSC page clocksource is suitable for vDSO, however, the protocol
defined by the hypervisor is different from VCLOCK_PVCLOCK. Implement the
required support by adding hvclock_page VVAR.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/entry/vdso/vclock_gettime.c | 36 +++++++++++++++++++++++++++++++++++
arch/x86/entry/vdso/vdso-layout.lds.S | 3 ++-
arch/x86/entry/vdso/vdso2c.c | 3 +++
arch/x86/entry/vdso/vma.c | 7 +++++++
arch/x86/hyperv/hv_init.c | 3 +++
arch/x86/include/asm/clocksource.h | 3 ++-
arch/x86/include/asm/vdso.h | 1 +
7 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index 9d4d6e1..4af10b4 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -17,6 +17,7 @@
#include <asm/unistd.h>
#include <asm/msr.h>
#include <asm/pvclock.h>
+#include <asm/mshyperv.h>
#include <linux/math64.h>
#include <linux/time.h>
#include <linux/kernel.h>
@@ -32,6 +33,11 @@ extern u8 pvclock_page
__attribute__((visibility("hidden")));
#endif

+#ifdef CONFIG_HYPERV_TSCPAGE
+extern u8 hvclock_page
+ __attribute__((visibility("hidden")));
+#endif
+
#ifndef BUILD_VDSO32

notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
@@ -141,6 +147,32 @@ static notrace u64 vread_pvclock(int *mode)
return last;
}
#endif
+#ifdef CONFIG_HYPERV_TSCPAGE
+static notrace u64 vread_hvclock(int *mode)
+{
+ const struct ms_hyperv_tsc_page *tsc_pg =
+ (const struct ms_hyperv_tsc_page *)&hvclock_page;
+ u64 sequence, scale, offset, current_tick, cur_tsc;
+
+ while (1) {
+ sequence = READ_ONCE(tsc_pg->tsc_sequence);
+ if (!sequence)
+ break;
+
+ scale = READ_ONCE(tsc_pg->tsc_scale);
+ offset = READ_ONCE(tsc_pg->tsc_offset);
+ rdtscll(cur_tsc);
+
+ current_tick = mul_u64_u64_shr(cur_tsc, scale, 64) + offset;
+
+ if (READ_ONCE(tsc_pg->tsc_sequence) == sequence)
+ return current_tick;
+ }
+
+ *mode = VCLOCK_NONE;
+ return 0;
+}
+#endif

notrace static u64 vread_tsc(void)
{
@@ -173,6 +205,10 @@ notrace static inline u64 vgetsns(int *mode)
else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
cycles = vread_pvclock(mode);
#endif
+#ifdef CONFIG_HYPERV_TSCPAGE
+ else if (gtod->vclock_mode == VCLOCK_HVCLOCK)
+ cycles = vread_hvclock(mode);
+#endif
else
return 0;
v = (cycles - gtod->cycle_last) & gtod->mask;
diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index a708aa9..8ebb4b6 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -25,7 +25,7 @@ SECTIONS
* segment.
*/

- vvar_start = . - 2 * PAGE_SIZE;
+ vvar_start = . - 3 * PAGE_SIZE;
vvar_page = vvar_start;

/* Place all vvars at the offsets in asm/vvar.h. */
@@ -36,6 +36,7 @@ SECTIONS
#undef EMIT_VVAR

pvclock_page = vvar_start + PAGE_SIZE;
+ hvclock_page = vvar_start + 2 * PAGE_SIZE;

. = SIZEOF_HEADERS;

diff --git a/arch/x86/entry/vdso/vdso2c.c b/arch/x86/entry/vdso/vdso2c.c
index 491020b..0780a44 100644
--- a/arch/x86/entry/vdso/vdso2c.c
+++ b/arch/x86/entry/vdso/vdso2c.c
@@ -74,6 +74,7 @@ enum {
sym_vvar_page,
sym_hpet_page,
sym_pvclock_page,
+ sym_hvclock_page,
sym_VDSO_FAKE_SECTION_TABLE_START,
sym_VDSO_FAKE_SECTION_TABLE_END,
};
@@ -82,6 +83,7 @@ const int special_pages[] = {
sym_vvar_page,
sym_hpet_page,
sym_pvclock_page,
+ sym_hvclock_page,
};

struct vdso_sym {
@@ -94,6 +96,7 @@ struct vdso_sym required_syms[] = {
[sym_vvar_page] = {"vvar_page", true},
[sym_hpet_page] = {"hpet_page", true},
[sym_pvclock_page] = {"pvclock_page", true},
+ [sym_hvclock_page] = {"hvclock_page", true},
[sym_VDSO_FAKE_SECTION_TABLE_START] = {
"VDSO_FAKE_SECTION_TABLE_START", false
},
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 10820f6..b256a3b 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -21,6 +21,7 @@
#include <asm/page.h>
#include <asm/desc.h>
#include <asm/cpufeature.h>
+#include <asm/mshyperv.h>

#if defined(CONFIG_X86_64)
unsigned int __read_mostly vdso64_enabled = 1;
@@ -120,6 +121,12 @@ static int vvar_fault(const struct vm_special_mapping *sm,
vmf->address,
__pa(pvti) >> PAGE_SHIFT);
}
+ } else if (sym_offset == image->sym_hvclock_page) {
+ struct ms_hyperv_tsc_page *tsc_pg = hv_get_tsc_page();
+
+ if (tsc_pg && vclock_was_used(VCLOCK_HVCLOCK))
+ ret = vm_insert_pfn(vma, vmf->address,
+ vmalloc_to_pfn(tsc_pg));
}

if (ret == 0 || ret == -EBUSY)
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 0ce8485..17519e0 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -157,6 +157,9 @@ void hyperv_init(void)
tsc_msr.guest_physical_address = vmalloc_to_pfn(tsc_pg);

wrmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr.as_uint64);
+
+ hyperv_cs_tsc.archdata.vclock_mode = VCLOCK_HVCLOCK;
+
clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
return;
}
diff --git a/arch/x86/include/asm/clocksource.h b/arch/x86/include/asm/clocksource.h
index eae33c7..47bea8c 100644
--- a/arch/x86/include/asm/clocksource.h
+++ b/arch/x86/include/asm/clocksource.h
@@ -6,7 +6,8 @@
#define VCLOCK_NONE 0 /* No vDSO clock available. */
#define VCLOCK_TSC 1 /* vDSO should use vread_tsc. */
#define VCLOCK_PVCLOCK 2 /* vDSO should use vread_pvclock. */
-#define VCLOCK_MAX 2
+#define VCLOCK_HVCLOCK 3 /* vDSO should use vread_hvclock. */
+#define VCLOCK_MAX 3

struct arch_clocksource_data {
int vclock_mode;
diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h
index 2444189..bccdf49 100644
--- a/arch/x86/include/asm/vdso.h
+++ b/arch/x86/include/asm/vdso.h
@@ -20,6 +20,7 @@ struct vdso_image {
long sym_vvar_page;
long sym_hpet_page;
long sym_pvclock_page;
+ long sym_hvclock_page;
long sym_VDSO32_NOTE_MASK;
long sym___kernel_sigreturn;
long sym___kernel_rt_sigreturn;
--
2.9.3