From: Stanislav Kinsburskii <skinsburskii@xxxxxxxxxxxxxxxxxxx> Sent: Friday, November 4, 2022 1:41 PM
>
> Microsoft Hypervisor root partition has to map the TSC page specified
> by the hypervisor, instead of providing the page to the hypervisor like
> it's done in the guest partitions.
>
> However, it's too early to map the page when the clock is initialized, so, the
> actual mapping is happening later.
>
> Signed-off-by: Stanislav Kinsburskiy <stanislav.kinsburskiy@xxxxxxxxx>
> CC: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
> CC: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu@xxxxxxxxxx>
> CC: Dexuan Cui <decui@xxxxxxxxxxxxx>
> CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> CC: Ingo Molnar <mingo@xxxxxxxxxx>
> CC: Borislav Petkov <bp@xxxxxxxxx>
> CC: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> CC: x86@xxxxxxxxxx
> CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
> CC: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> CC: linux-hyperv@xxxxxxxxxxxxxxx
> CC: linux-kernel@xxxxxxxxxxxxxxx
> ---
> arch/x86/hyperv/hv_init.c | 2 ++
> drivers/clocksource/hyperv_timer.c | 44 +++++++++++++++++++++++++++++-------
> include/clocksource/hyperv_timer.h | 1 +
> 3 files changed, 38 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index f49bc3ec76e6..89954490af93 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -464,6 +464,8 @@ void __init hyperv_init(void)
> BUG_ON(!src);
> memcpy_to_page(pg, 0, src, HV_HYP_PAGE_SIZE);
> memunmap(src);
> +
> + hv_remap_tsc_clocksource();
> } else {
> hypercall_msr.guest_physical_address =
> vmalloc_to_pfn(hv_hypercall_pg);
> wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> index 9445a1558fe9..c0cef92b12b8 100644
> --- a/drivers/clocksource/hyperv_timer.c
> +++ b/drivers/clocksource/hyperv_timer.c
> @@ -509,9 +509,6 @@ static bool __init hv_init_tsc_clocksource(void)
> if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
> return false;
>
> - if (hv_root_partition)
> - return false;
> -
> /*
> * If Hyper-V offers TSC_INVARIANT, then the virtualized TSC correctly
> * handles frequency and offset changes due to live migration,
> @@ -529,16 +526,28 @@ static bool __init hv_init_tsc_clocksource(void)
> }
>
> hv_read_reference_counter = read_hv_clock_tsc;
> - tsc_pfn = HVPFN_DOWN(virt_to_phys(tsc_page));
>
> /*
> - * The Hyper-V TLFS specifies to preserve the value of reserved
> - * bits in registers. So read the existing value, preserve the
> - * low order 12 bits, and add in the guest physical address
> - * (which already has at least the low 12 bits set to zero since
> - * it is page aligned). Also set the "enable" bit, which is bit 0.
> + * TSC page mapping works differently in root compared to guest.
> + * - In guest partition the guest PFN has to be passed to the
> + * hypervisor.
> + * - In root partition it's other way around: it has to map the PFN
> + * provided by the hypervisor.
> + * But it can't be mapped right here as it's too early and MMU isn't
> + * ready yet. So, we only set the enable bit here and will remap the
> + * page later in hv_remap_tsc_clocksource().
> + *
> + * It worth mentioning, that TSC clocksource read function
> + * (read_hv_clock_tsc) has a MSR-based fallback mechanism, used when
> + * TSC page is zeroed (which is the case until the PFN is remapped) and
> + * thus TSC clocksource will work even without the real TSC page
> + * mapped.
> */
> tsc_msr.as_uint64 = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> + if (hv_root_partition)
> + tsc_pfn = tsc_msr.pfn;
> + else
> + tsc_pfn = HVPFN_DOWN(virt_to_phys(tsc_page));
> tsc_msr.enable = 1;
> tsc_msr.pfn = tsc_pfn;
> hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr.as_uint64);
> @@ -573,3 +582,20 @@ void __init hv_init_clocksource(void)
> hv_sched_clock_offset = hv_read_reference_counter();
> hv_setup_sched_clock(read_hv_sched_clock_msr);
> }
> +
> +void __init hv_remap_tsc_clocksource(void)
> +{
> + if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
> + return;
> +
> + if (!hv_root_partition) {
> + WARN(1, "%s: attempt to remap TSC page in guest partition\n",
> + __func__);
> + return;
> + }
> +
> + tsc_page = memremap(tsc_pfn << HV_HYP_PAGE_SHIFT, sizeof(tsc_pg),
> + MEMREMAP_WB);
> + if (!tsc_page)
> + pr_err("Failed to remap Hyper-V TSC page.\n");
> +}
> diff --git a/include/clocksource/hyperv_timer.h
> b/include/clocksource/hyperv_timer.h
> index 3078d23faaea..783701a2102d 100644
> --- a/include/clocksource/hyperv_timer.h
> +++ b/include/clocksource/hyperv_timer.h
> @@ -31,6 +31,7 @@ extern void hv_stimer_global_cleanup(void);
> extern void hv_stimer0_isr(void);
>
> extern void hv_init_clocksource(void);
> +extern void hv_remap_tsc_clocksource(void);
>
> extern unsigned long hv_get_tsc_pfn(void);
> extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
>
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
