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authorAndrey Smetanin <asmetanin@virtuozzo.com>2015-12-14 16:01:55 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-12-14 19:15:05 -0800
commitc35b82ef0294ae5052120615f5cfcef17c5a6bf7 (patch)
tree25b78f6815b620598fc284e1342c0b65bd5f37b1 /drivers/hv
parent8599846d73997cdbccf63f23394d871cfad1e5e6 (diff)
drivers/hv: correct tsc page sequence invalid value
Hypervisor Top Level Functional Specification v3/4 says that TSC page sequence value = -1(0xFFFFFFFF) is used to indicate that TSC page no longer reliable source of reference timer. Unfortunately, we found that Windows Hyper-V guest side implementation uses sequence value = 0 to indicate that Tsc page no longer valid. This is clearly visible inside Windows 2012R2 ntoskrnl.exe HvlGetReferenceTime() function dissassembly: HvlGetReferenceTime proc near xchg ax, ax loc_1401C3132: mov rax, cs:HvlpReferenceTscPage mov r9d, [rax] test r9d, r9d jz short loc_1401C3176 rdtsc mov rcx, cs:HvlpReferenceTscPage shl rdx, 20h or rdx, rax mov rax, [rcx+8] mov rcx, cs:HvlpReferenceTscPage mov r8, [rcx+10h] mul rdx mov rax, cs:HvlpReferenceTscPage add rdx, r8 mov ecx, [rax] cmp ecx, r9d jnz short loc_1401C3132 jmp short loc_1401C3184 loc_1401C3176: mov ecx, 40000020h rdmsr shl rdx, 20h or rdx, rax loc_1401C3184: mov rax, rdx retn HvlGetReferenceTime endp This patch aligns Tsc page invalid sequence value with Windows Hyper-V guest implementation which is more compatible with both Hyper-V hypervisor and KVM hypervisor. Signed-off-by: Andrey Smetanin <asmetanin@virtuozzo.com> Signed-off-by: Denis V. Lunev <den@openvz.org> CC: "K. Y. Srinivasan" <kys@microsoft.com> CC: Haiyang Zhang <haiyangz@microsoft.com> CC: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Denis V. Lunev <den@openvz.org> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/hv')
-rw-r--r--drivers/hv/hv.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index eb4e383dbc58..11bca51ef5ff 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -140,7 +140,7 @@ static cycle_t read_hv_clock_tsc(struct clocksource *arg)
cycle_t current_tick;
struct ms_hyperv_tsc_page *tsc_pg = hv_context.tsc_page;
- if (tsc_pg->tsc_sequence != -1) {
+ if (tsc_pg->tsc_sequence != 0) {
/*
* Use the tsc page to compute the value.
*/
@@ -162,7 +162,7 @@ static cycle_t read_hv_clock_tsc(struct clocksource *arg)
if (tsc_pg->tsc_sequence == sequence)
return current_tick;
- if (tsc_pg->tsc_sequence != -1)
+ if (tsc_pg->tsc_sequence != 0)
continue;
/*
* Fallback using MSR method.