From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E190E3BFE4D; Mon, 17 Aug 2026 08:15:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786954506; cv=none; b=BR/5SUowZ9UAjMd6EFXLzQPp1cNoqq997hH5MSElsXsJIxwE1lwMeC696ud5HT5V9HS+ieWeK+yDivjfY8D+zKawsyaiHeCoX1lMnxOZMim4uO3bzAQtxx05Ca4x7DgNVqmP9kuWRv48F998k16e5TOB3WV7tqVezNfsMhH2Fng= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786954506; c=relaxed/simple; bh=5IaM7S8pJ4l+BbbzLOSDCtz6n0ukN2INohqP14kRShQ=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=hB9yJYp302PGzSMVbcmtoFIQsfORD8LXjy4kE2+KhhRsVTqieZkMIynf1tS0i8VzXLmSQ2gbh6t/g7KXUjnDnbIJxnkBrpteQJT4aZDrS2ceV26ch2s0oFI4spNnGML4TChfv6hN1THztZwC2ARLYq4O9VAgJ9x8luHIcJx9ONE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=efU2Bq/p; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="efU2Bq/p" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 80B401F000E9; Mon, 17 Aug 2026 08:15:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786954505; bh=LCgCrZXgCdArZmf2yiPTxV0mnMn5mMjdKKPHJnTTlIw=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=efU2Bq/pLLMIEug1UJukJ7+g9bFkWuGEnnmiKL4Ej46g3nqlaQeRgvFoHLTDiifCQ K4gwXgwYHL+kY/ilgjSfolKArqppSdiDkJmHGqougrJB3RDGwtntuyd5jOgJTPLWD0 cPqUo3qLflUWODuZPgJto+MYOT6XjM2UGljj7AMj36riAH/9wFJ76QBXyPvyy5/Vhn nbHFBDZPW0iEFG7gsk9vG4bHMWWKEeb7Wylr+0dbWSR1ZL2JqDHl8JR1NWsB2+b/Th 9iUMx/3vkauHQEbgN6ovA0bn6R8tr3TV+PM8MMQZ8jx6e7Id+hSWGw7zJGkmD0Liu8 tJ5Y7WHahaQhA== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wvsUp-0000000GCDn-0C2T; Mon, 17 Aug 2026 08:15:03 +0000 Date: Mon, 17 Aug 2026 09:15:02 +0100 Message-ID: <86tsotyxh5.wl-maz@kernel.org> From: Marc Zyngier To: Dongli Zhang Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-kselftest@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, oupton@kernel.org, fuad.tabba@linux.dev, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, dwmw2@infradead.org, joe.jin@oracle.com Subject: Re: [PATCH 0/4] KVM: Reset steal time accounting on vCPU pid change (x86 and arm64) In-Reply-To: <20260816053630.527528-1-dongli.zhang@oracle.com> References: <20260816053630.527528-1-dongli.zhang@oracle.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: dongli.zhang@oracle.com, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-kselftest@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, oupton@kernel.org, fuad.tabba@linux.dev, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, dwmw2@infradead.org, joe.jin@oracle.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Sun, 16 Aug 2026 06:33:01 +0100, Dongli Zhang wrote: [...] > 4. Guest kernel changes are not included. I may send it separately to keep > this series limited to the KVM hypervisor. Hold on. Do you mean you are changing the guest visible behaviour of a PV interface? That's an ABI. It *cannot* change unilaterally. > > [PATCH 1/5] x86/kvm: Reset prev_steal_time and prev_steal_time_rq when enabling steal time > https://lore.kernel.org/all/20260505003044.78693-2-dongli.zhang@oracle.com > > 5. There is one remaining corner case: this series resets last_steal when > the vCPU run PID changes, but not when steal time is enabled. If additional > host run_delay is accumulated after the PID changes but before the guest > enables steal time, that delta could be unexpectedly accounted to guest > vCPU steal time. In practice, this should not happen for Linux guests. Why is Linux immune to this? Also, KVM does not cater for Linux guests only. M. -- Without deviation from the norm, progress is not possible.