From 0408f16b43e578e70ad12a857159a0a771cfaa7c Mon Sep 17 00:00:00 2001 From: Stanislav Kinsburskiy Date: Fri, 4 Nov 2022 20:40:55 +0000 Subject: clocksource: hyper-v: Add TSC page support for root partition 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 CC: "K. Y. Srinivasan" CC: Haiyang Zhang CC: Wei Liu CC: Dexuan Cui CC: Thomas Gleixner CC: Ingo Molnar CC: Borislav Petkov CC: Dave Hansen CC: x86@kernel.org CC: "H. Peter Anvin" CC: Daniel Lezcano CC: linux-hyperv@vger.kernel.org CC: linux-kernel@vger.kernel.org Reviewed-by: Michael Kelley Reviewed-by: Anirudh Rayabharam Link: https://lore.kernel.org/r/166759443644.385891.15921594265843430260.stgit@skinsburskii-cloud-desktop.internal.cloudapp.net Signed-off-by: Wei Liu --- drivers/clocksource/hyperv_timer.c | 44 ++++++++++++++++++++++++++++++-------- 1 file changed, 35 insertions(+), 9 deletions(-) (limited to 'drivers/clocksource') 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"); +} -- cgit v1.2.3