From patchwork Sat Apr 27 11:05:09 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Woodhouse X-Patchwork-Id: 13645631 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E2C844A990; Sat, 27 Apr 2024 11:19:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714216786; cv=none; b=Uu45iypOnsm9fjwx6DhN4r/WhHGqUOiGt9gNFN8FvIEaJ1egwt+IX5saS0MzRzzCy/2h3mamyMAYkyqsT0sDQVLPSXHYrthYIBHxnkfSPFPTDYcVXuS1Cgl44FyeH4deJAR15WMyqDXjYpowlPeLE1iG/b1NbuYSM8xyicd8kt4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714216786; c=relaxed/simple; bh=HCznYAv0EfRhddfdK9swdqfYALkzcbaaWAuEQfAFYNA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jGUUuJQdQJIgr/D81jHtkA/pnUOGl1nLOjgl7o4guvK5VN2+5oDZq/4BZ21Id8sL7usJ2n3YxO5a9U/00TGHk4UaaqxjQMJ1xkX6VNSOh4fq6pkZJZnLGqOTq29B6aeZ+wyiMuH47kDLlOG2vBwKolL7lW4LQK89Ch7rR7piVyQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=casper.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=nTm+vxkF; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=casper.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="nTm+vxkF" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Sender:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description; bh=rpfo1oUoJzRPiJFA+UCmdgAFooGLVsmHebsz9FfSOoc=; b=nTm+vxkFhMhl43Kyx8J2RVas/v MgEFbuFINgZfn9jT60qo3mU4baGpwZJVcBIjpTR4Do3kWwZT4QUBg98PbOUoDJbLq3/nZD2OY7Lis 4qNu3jtQVa5vX8YsbzMFJANZWuxcIiGKD1NvVLPedn4jVv5MiY61D62uG2blUJhPWmq61mf8bx3cK Ox6xzXad8RByBaQdzoUhz+qkrlva0R8I8ybhudiaPmkY8jntMPVkIDd+4/PMdMM16Ko/VrzBT0Q+X Cnr2IMYNucMM9bhDwMYaF7Qlp3kvX5HrFhfJtQqIIGOH65r+DNSlQJGm4vBEmm7hlgAA4EKhZ4yNR 1bHXGHQg==; Received: from [2001:8b0:10b:1::ebe] (helo=i7.infradead.org) by casper.infradead.org with esmtpsa (Exim 4.97.1 #2 (Red Hat Linux)) id 1s0g5h-00000007Jwp-00lT; Sat, 27 Apr 2024 11:19:37 +0000 Received: from dwoodhou by i7.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1s0g5g-000000002bl-2B7U; Sat, 27 Apr 2024 12:19:36 +0100 From: David Woodhouse To: kvm@vger.kernel.org Cc: Paolo Bonzini , Jonathan Corbet , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paul Durrant , Shuah Khan , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Oliver Upton , Marcelo Tosatti , jalliste@amazon.co.uk, sveith@amazon.de, zide.chen@intel.com, Dongli Zhang Subject: [PATCH v2 12/15] KVM: x86: Improve synchronization in kvm_synchronize_tsc() Date: Sat, 27 Apr 2024 12:05:09 +0100 Message-ID: <20240427111929.9600-13-dwmw2@infradead.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240427111929.9600-1-dwmw2@infradead.org> References: <20240427111929.9600-1-dwmw2@infradead.org> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Sender: David Woodhouse X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html From: David Woodhouse When synchronizing to an existing TSC (either by explicitly writing zero, or the legacy hack where the TSC is written within one second's worth of the previously written TSC), the last_tsc_write and last_tsc_nsec values were being misrecorded by __kvm_synchronize_tsc(). The *unsynchronized* value of the TSC (perhaps even zero) was bring recorded, along with the current time at which kvm_synchronize_tsc() was called. This could cause *subsequent* writes to fail to synchronize correctly. Fix that by resetting {data, ns} to the previous values before passing them to __kvm_synchronize_tsc() when synchronization is detected. Except in the case where the TSC is unstable and *has* to be synthesised from the host clock, in which case attempt to create a nsec/tsc pair which is on the correct line. Furthermore, there were *three* different TSC reads used for calculating the "current" time, all slightly different from each other. Fix that by using kvm_get_time_and_clockread() where possible and using the same host_tsc value in all cases. Signed-off-by: David Woodhouse --- arch/x86/kvm/x86.c | 32 ++++++++++++++++++++++++++++---- 1 file changed, 28 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index ea59694d712a..6ec43f39bdb0 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -201,6 +201,10 @@ module_param(eager_page_split, bool, 0644); static bool __read_mostly mitigate_smt_rsb; module_param(mitigate_smt_rsb, bool, 0444); +#ifdef CONFIG_X86_64 +static bool kvm_get_time_and_clockread(s64 *kernel_ns, u64 *tsc_timestamp); +#endif + /* * Restoring the host value for MSRs that are only consumed when running in * usermode, e.g. SYSCALL MSRs and TSC_AUX, can be deferred until the CPU @@ -2753,14 +2757,22 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 *user_value) { u64 data = user_value ? *user_value : 0; struct kvm *kvm = vcpu->kvm; - u64 offset, ns, elapsed; + u64 offset, host_tsc, ns, elapsed; unsigned long flags; bool matched = false; bool synchronizing = false; +#ifdef CONFIG_X86_64 + if (!kvm_get_time_and_clockread(&ns, &host_tsc)) +#endif + { + ns = get_kvmclock_base_ns(); + host_tsc = rdtsc(); + } + raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags); - offset = kvm_compute_l1_tsc_offset(vcpu, rdtsc(), data); - ns = get_kvmclock_base_ns(); + + offset = kvm_compute_l1_tsc_offset(vcpu, host_tsc, data); elapsed = ns - kvm->arch.last_tsc_nsec; if (vcpu->arch.virtual_tsc_khz) { @@ -2805,12 +2817,24 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 *user_value) */ if (synchronizing && vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) { + /* + * If synchronizing, the "last written" TSC value/time recorded + * by __kvm_synchronize_tsc() should not change (i.e. should + * be precisely the same as the existing generation)... + */ + data = kvm->arch.last_tsc_write; + if (!kvm_check_tsc_unstable()) { offset = kvm->arch.cur_tsc_offset; + ns = kvm->arch.cur_tsc_nsec; } else { + /* + * ... unless the TSC is unstable and has to be + * synthesised from the host clock in nanoseconds. + */ u64 delta = nsec_to_cycles(vcpu, elapsed); data += delta; - offset = kvm_compute_l1_tsc_offset(vcpu, rdtsc(), data); + offset = kvm_compute_l1_tsc_offset(vcpu, host_tsc, data); } matched = true; }