> -----Original Message-----
> From: Denis V. Lunev [mailto:d...@openvz.org]
> Sent: Monday, November 2, 2015 3:34 AM
> Cc: rka...@virtuozzo.com; de...@linuxdriverproject.org; linux-
> ker...@vger.kernel.org; Andrey Smetanin <asmeta...@virtuozzo.com>; KY
> Srinivasan <k...@microsoft.com>; Haiyang Zhang
> <haiya...@microsoft.com>; Vitaly Kuznetsov <vkuzn...@redhat.com>;
> Denis V. Lunev <d...@openvz.org>
> Subject: [PATCH 1/1] drivers/hv: correct tsc page sequence invalid value
>
> From: Andrey Smetanin <asmeta...@virtuozzo.com>
>
> 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 that Tsc page no longer valid.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 <asmeta...@virtuozzo.com>
> CC: "K. Y. Srinivasan" <k...@microsoft.com>
Thanks Andrey; the Hyper-V team will be updating the Hyper-V documentation.
Acked-by: K. Y. Srinivasan <k...@microsoft.com>
Regards,
K. Y
> CC: Haiyang Zhang <haiya...@microsoft.com>
> CC: Vitaly Kuznetsov <vkuzn...@redhat.com>
>
> TARGET: Microsoft Hyper-V Linux guest drivers
> Signed-off-by: Denis V. Lunev <d...@openvz.org>
> ---
> 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 6341be8..68d0701 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -139,7 +139,7 @@ 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.
> */
> @@ -161,7 +161,7 @@ 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.
> --
> 2.1.4
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