From c35b82ef0294ae5052120615f5cfcef17c5a6bf7 Mon Sep 17 00:00:00 2001 From: Andrey Smetanin Date: Mon, 14 Dec 2015 16:01:55 -0800 Subject: [PATCH] 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we found that Windows Hyper-V guest side implementation uses sequence value = 0 to indicate that Tsc page no longer valid.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 Signed-off-by: Denis V. Lunev CC: "K. Y. Srinivasan" CC: Haiyang Zhang CC: Vitaly Kuznetsov Signed-off-by: Denis V. Lunev Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman --- drivers/hv/hv.c | 4 ++-- 1 file 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. -- 2.30.2