From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4C4EA48B38F for ; Wed, 26 Aug 2026 21:33:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787780011; cv=none; b=cdZvx8aScGTRVWe/EBS4YT46015LJKymculLHmLzEq4V/98rnZANNjSzw/bn2CKEo2lKNOZvfVj/Ugb0CVrULvlm3rFwfoyhGJIYL0xZVEEkKhM3d1U+txWN4b2vUDevT8Dyt5gilYhIWi56Zgt4x7EJ5jPlKXh6zgbA3Y8f+l0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787780011; c=relaxed/simple; bh=x9kqdAvWcySW/UFriv/XVSVV3wGHtlM1R1TTiEGvaKc=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Md//l8V3Wnza6WTvtyFKbNVrxcUM+Yq4pEaD3/TrY3n0seAlaeOorA9l3W6GSqukCt3LbWV+vSbVj5816w8De78jvZFAX4LBllpjqKByYSvve7hBParUkmTUs4sqiJ/25MhXCQSJ0Lx3RetY4klYBtxs9MMb1FSiqzrFg8oJOwI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=a9raJv3u; arc=none smtp.client-ip=209.85.215.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="a9raJv3u" Received: by mail-pg1-f199.google.com with SMTP id 41be03b00d2f7-cc1bbd7d6e6so1629842a12.3 for ; Wed, 26 Aug 2026 14:33:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1787780006; x=1788384806; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:from:to:cc:subject:date:message-id :reply-to:content-type; bh=hxtXNEiVVHLTLVeOZPmDmbDA/5ZmZ/osRSTz6+H5aOI=; b=a9raJv3uywLEr3mXX36hLeUFvym8VC7a7qo212DBcpJKiXUnv6jx32p0c1hc1ErjXR OZzXJ8TDdLWKe5azUuDFfaqsjgIv+qykEAePUeKiwnDhubXYyVe3J6s/v5TRBzPUCJOZ ieqq7ynBEioOeSIZP9Mwty/0ZWpqP0KGSDHvaemZCHtHTroOd2SrmAfI9wBa6dx64xzN RelR/hSVsAggpgtYra1EL27ULVeQtHc7ExpmJl9+3xr5yPFcDzrW6w1zAzCXre+iSqn8 iZ5IoMkNLt8ad19YHizBNqaDpUE9K+B7JnGMMd025LT9l5P7QvCpSTy2vGhKNq3ZDnZV GwUw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787780006; x=1788384806; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to:content-type; bh=hxtXNEiVVHLTLVeOZPmDmbDA/5ZmZ/osRSTz6+H5aOI=; b=bJ8VaH8x2TUPFyankzIgL7TxeaMswXXWgZdxbeYE7VD8F7eYL5nSuUViF13EiF0Odv Ju10VzRPTRgvNLZpHGyKYfAQ7o1zGhHDvt3xY8U98y1AZtS3/+euXBoro6zjp26AUiuU 1xXTPtnD2I2OnPU7zbi2GzWX6hI0c3Z4MdI6355hBNibCnnaOlXY8eD8TgMQvmvJTPco eE44WXsPJSuj8U53t2ZcWuSChf1mtPEdRABYA8kZwo7q5xrQ9bRwv2zl5PaATNkmeIwL pqNfTerIP3l9vlNOXhJ5f71iq6eXiVC66DoQIlDGZTJQryFbGBMSGESyK8ukWc5r5H1/ ITBw== X-Forwarded-Encrypted: i=1; AHgh+Rp5qTvvKTM4+i3APpJVZit/VtefmXeHS1IR07Gjr7fCbYUMSEIxsKmqmAB20qVH1AuComO2A2s6PCTsgJE=@vger.kernel.org X-Gm-Message-State: AFuF++nzSiCfENbgyaoXrPxWl+HMM8X1fYXoZvLhXGnucWcnAIOmHIqI xTlGparFxz6//bVyGNR6mJ4EI8JSdqklIbB1I0tLzzODwZOxAiVTOUO/9DMHKK5orDBAUY9C99H nJ9mPlw== X-Received: from pfux28.prod.google.com ([2002:a05:6a00:bdc:b0:84a:3bc9:3bcd]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:4f92:b0:848:2e3c:9955 with SMTP id d2e1a72fcca58-85371fa599amr17200089b3a.4.1787780006189; Wed, 26 Aug 2026 14:33:26 -0700 (PDT) Reply-To: Sean Christopherson Date: Wed, 26 Aug 2026 14:32:59 -0700 In-Reply-To: <20260826213303.914988-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260826213303.914988-1-seanjc@google.com> X-Mailer: git-send-email 2.55.0.887.g758fc8c411-goog Message-ID: <20260826213303.914988-20-seanjc@google.com> Subject: [PATCH v10 19/21] KVM: x86: Use kernel timekeeping snapshots for getting kvmclock time since boot From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Paul Durrant , David Woodhouse , Dongli Zhang Content-Type: text/plain; charset="UTF-8" From: David Woodhouse Replace the KVM-private vgettsc()+do_kvmclock_base() timekeeping reimplementation with calls to the recently crafted, generic ktime_get_snapshot_id() interface. This is the first step towards dropping KVM's homebrewed implementation entirely (do_monotonic() and do_realtime() will be converted in the near future). As with KVM's implementation, the snapshot provides both the system time and the raw_cycles (TSC), atomically paired using a sequence counter. The equivalents to vgettsc()'s TSC and HVCLOCK modes respectively are if the clocksource itself is TSC (cs_id == CSID_X86_TSC) and if the underlying hardware clocksource is TSC (hw_csid == CSID_X86_TSC). In the Hyper-V case, i.e. hw_csid == CSID_X86_TSC, if the clocksource couldn't provide a raw hardware counter value, treat the clock not being based on TSC, which which is equivalent to vgettsc() returning VDSO_CLOCKMODE_NONE. Unlike KVM's current implementation, don't include offs_boot in the atomically-acquired tuple as there's simply no need to do so: the time since boot only changes at boot (duh) and at suspend/resume boundaries. Unless processes aren't being frozen/thawed before/after suspend/resume, which would completely break suspend/resume, TK_OFFS_BOOT can't change while kvm_get_time_and_clockread() is running. And if KVM does somehow try to take a snapshot during suspend, timekeeping core will WARN and refuse to provide the snapshot. This is a step towards eliminating the pvclock_gtod_data private copy of timekeeping state and the associated notifier callback. Signed-off-by: David Woodhouse [sean: separate from other conversions, massage changelog accordingly] Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 57 ++++++++++++++++++++++++---------------------- 1 file changed, 30 insertions(+), 27 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 51a8250e758b..32390b20a2b4 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -35,6 +35,7 @@ #include "smm.h" #include +#include #include #include #include @@ -1437,29 +1438,6 @@ static inline u64 vgettsc(struct pvclock_clock *clock, u64 *tsc_timestamp, return v * clock->mult; } -/* - * As with get_kvmclock_base_ns(), this counts from boot time, at the - * frequency of CLOCK_MONOTONIC_RAW (hence adding gtos->offs_boot). - */ -static int do_kvmclock_base(s64 *t, u64 *tsc_timestamp) -{ - struct pvclock_gtod_data *gtod = &pvclock_gtod_data; - unsigned long seq; - int mode; - u64 ns; - - do { - seq = read_seqcount_begin(>od->seq); - ns = gtod->raw_clock.base_cycles; - ns += vgettsc(>od->raw_clock, tsc_timestamp, &mode); - ns >>= gtod->raw_clock.shift; - ns += ktime_to_ns(ktime_add(gtod->raw_clock.offset, gtod->offs_boot)); - } while (unlikely(read_seqcount_retry(>od->seq, seq))); - *t = ns; - - return mode; -} - /* * This calculates CLOCK_MONOTONIC at the time of the TSC snapshot, with * no boot time offset. @@ -1504,6 +1482,29 @@ static int do_realtime(struct timespec64 *ts, u64 *tsc_timestamp) return mode; } +static bool kvm_snapshot_has_tsc(struct system_time_snapshot *snap, + u64 *tsc_timestamp) +{ + /* + * ktime_get_snapshot_id() cannot fail for standard clock IDs + * (only for invalid/aux clocks or during suspend, with a WARN). + */ + if (!snap->valid) + return false; + + if (snap->cs_id == CSID_X86_TSC) { + *tsc_timestamp = snap->cycles; + return true; + } + + if (snap->hw_csid == CSID_X86_TSC && snap->hw_cycles) { + *tsc_timestamp = snap->hw_cycles; + return true; + } + + return false; +} + /* * Calculates the kvmclock_base_ns (CLOCK_MONOTONIC_RAW + boot time) and * reports the TSC value from which it do so. Returns true if host is @@ -1511,12 +1512,14 @@ static int do_realtime(struct timespec64 *ts, u64 *tsc_timestamp) */ static bool kvm_get_time_and_clockread(s64 *kernel_ns, u64 *tsc_timestamp) { - /* checked again under seqlock below */ - if (!gtod_is_based_on_tsc(pvclock_gtod_data.clock.vclock_mode)) + struct system_time_snapshot snap = {}; + + ktime_get_snapshot_id(CLOCK_MONOTONIC_RAW, &snap); + if (!kvm_snapshot_has_tsc(&snap, tsc_timestamp)) return false; - return gtod_is_based_on_tsc(do_kvmclock_base(kernel_ns, - tsc_timestamp)); + *kernel_ns = ktime_to_ns(ktime_mono_to_any(snap.systime, TK_OFFS_BOOT)); + return true; } /* -- 2.55.0.887.g758fc8c411-goog