From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-167.mta0.migadu.com [91.218.175.167]) (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 8DADF3CB91E for ; Sun, 27 Sep 2026 07:53:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.167 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790495608; cv=none; b=rBIY8bphRVtb75EDkcaQcANjYyg6XH1tOq3fWjyDApl9DKmHuM6tFXYpcM9yuDp1X0QWO76ClY1w6mT1svMYDHo7jLZF3oyAnfwu3cwRKb3lDAcaDCvVaYnkeCwOkOQBx2/cpU50fEmigiT0N5VNGLF5gXhWX8lUwYp14LPfZHU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790495608; c=relaxed/simple; bh=yF7LfwdzDGXjHphjLzV953Ax0pwRq9FtyPOygII0oew=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=MtCtes6gv1tCYoOmk8ZmlYb3FeMlI6ZbOsBtG2BPXUkEfgKWXiTHJ1tnprZRTo71YhkKrbhwaoHXRdgQPyyOGNdifGuUewQYIyZYgAKpNDTqfK2z9DatBLnmFFp3B5LfEtg6rmw0jp7gjWE248aNOUWocjiO5tDPkrVlQIrPuT8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=DyL0Jxzj; arc=none smtp.client-ip=91.218.175.167 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="DyL0Jxzj" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=yF7LfwdzDGXjHphjLzV953Ax0pwRq9FtyPOygII0oew=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790495601; v=1; x=1791100401; b=DyL0JxzjPvzCfcdd7kDtT+jDp8wsIvruEM3bVcdKW4FB9qb7BRt1TTfe/sBJatxm4EosURZx 4V8Bk2CFv4zdJNfIrkol2NIeBhGhf7ODqairF1/L1QO4H2rk9xAbr1duiEHVqxhX/bUXddX63Xs 0Px5vQaS8u2Gt9mFqQ8RPavI= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 9517acd8b46f1144; Sun, 27 Sep 2026 07:53:21 +0000 X-Mizu-Trace-ID: 9517acd8b46f1144 X-Migadu-Flow: FLOW_OUT From: Tao Cui To: maobibo@loongson.cn, gaosong@loongson.cn, zhaotianrui@loongson.cn Cc: loongarch@lists.linux.dev, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, chenhuacai@kernel.org, kernel@xen0n.name, nagachaithanya9911@gmail.com, cui.tao@linux.dev, Tao Cui Subject: [PATCH 4/6] LoongArch: KVM: Rebase steal time counter in vcpu context Date: Sun, 27 Sep 2026 15:52:38 +0800 Message-ID: <20260927075240.3007947-5-cui.tao@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260927075240.3007947-1-cui.tao@linux.dev> References: <20260927075240.3007947-1-cui.tao@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tao Cui KVM_SET_DEVICE_ATTR(PVTIME GPA) initializes st.last_steal from the ioctl thread's run_delay, but kvm_update_stolen_time() accumulates the vcpu thread's run_delay; the first delta can be negative and wraps in u64, so the guest reads a steal time close to 2^64. Drop the initialization from the attr path and lazily rebase the counter on the first steal update, which runs in vcpu context like the hypercall path. Re-registering a GPA clears the rebase sentinel first and publishes the address with a write barrier; the reader side loads the address and sentinel with READ_ONCE and a read barrier so a concurrent re-registration is not observed half-applied. Fixes: b4ba157044ea ("LoongArch: KVM: Add PV steal time support in host side") Signed-off-by: Tao Cui --- arch/loongarch/kvm/vcpu.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c index 8e028be3f0a9..d931a5a802f6 100644 --- a/arch/loongarch/kvm/vcpu.c +++ b/arch/loongarch/kvm/vcpu.c @@ -154,12 +154,13 @@ static void kvm_update_stolen_time(struct kvm_vcpu *vcpu) u32 version; u64 steal; gpa_t gpa; + u64 last_steal; struct kvm_memslots *slots; struct kvm_steal_time __user *st; struct gfn_to_hva_cache *ghc; ghc = &vcpu->arch.st.cache; - gpa = vcpu->arch.st.guest_addr; + gpa = READ_ONCE(vcpu->arch.st.guest_addr); if (!(gpa & KVM_STEAL_PHYS_VALID)) return; @@ -187,8 +188,14 @@ static void kvm_update_stolen_time(struct kvm_vcpu *vcpu) smp_wmb(); unsafe_get_user(steal, &st->steal, out); - steal += current->sched_info.run_delay - vcpu->arch.st.last_steal; - vcpu->arch.st.last_steal = current->sched_info.run_delay; + /* acquire pairs with the smp_wmb in the attr path */ + smp_rmb(); + last_steal = READ_ONCE(vcpu->arch.st.last_steal); + if (!last_steal) + /* first update in vcpu context: rebase the counter */ + last_steal = current->sched_info.run_delay; + steal += current->sched_info.run_delay - last_steal; + WRITE_ONCE(vcpu->arch.st.last_steal, current->sched_info.run_delay); unsafe_put_user(steal, &st->steal, out); smp_wmb(); @@ -1122,7 +1129,7 @@ static int kvm_loongarch_pvtime_get_attr(struct kvm_vcpu *vcpu, || attr->attr != KVM_LOONGARCH_VCPU_PVTIME_GPA) return -ENXIO; - gpa = vcpu->arch.st.guest_addr; + gpa = READ_ONCE(vcpu->arch.st.guest_addr); if (put_user(gpa, user)) return -EFAULT; @@ -1197,7 +1204,7 @@ static int kvm_loongarch_pvtime_set_attr(struct kvm_vcpu *vcpu, return -EINVAL; if (!(gpa & KVM_STEAL_PHYS_VALID)) { - vcpu->arch.st.guest_addr = gpa; + WRITE_ONCE(vcpu->arch.st.guest_addr, gpa); return 0; } @@ -1208,8 +1215,10 @@ static int kvm_loongarch_pvtime_set_attr(struct kvm_vcpu *vcpu, srcu_read_unlock(&kvm->srcu, idx); if (!ret) { - vcpu->arch.st.guest_addr = gpa; - vcpu->arch.st.last_steal = current->sched_info.run_delay; + WRITE_ONCE(vcpu->arch.st.last_steal, 0); + /* publish the new address only after clearing the rebase sentinel */ + smp_wmb(); + WRITE_ONCE(vcpu->arch.st.guest_addr, gpa); kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu); } @@ -1800,7 +1809,7 @@ static void kvm_vcpu_set_pv_preempted(struct kvm_vcpu *vcpu) struct kvm_memslots *slots; struct kvm_steal_time __user *st; - gpa = vcpu->arch.st.guest_addr; + gpa = READ_ONCE(vcpu->arch.st.guest_addr); if (!(gpa & KVM_STEAL_PHYS_VALID)) return; -- 2.43.0