From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793191960; b=UEGT8L6ZGMx7sdZ2LSezy7Pp9FmuXmFLMy0KtNEHlu71QAT6Fg0luD+gNHbwUlTPp1uh 9l6x/V0B4x2JaXoiYWZU/e6UbCD3iyiSQCNfTZA5/8Gnftlf4fxHdlfEnRKUNNv9fmHV5 9t5gbfSbAdQGLkKVLhg7Yt2mA2RMtv66ws3cwqJKMeD0oHej3QzD8SLuXmSjjGtw5eEGh EyDGeUElkunHhyxXlJ7nehCHSSEQPXxswULbPXTIIoGvzS20g6CeH/OqgH1hzri/Gzhvw y0Y3h20VvZAbvfQ3+yaLkacq+084yfabBAsi/CEQ79y3hFCfVaQ0nWxpMOfRQKqgB0g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793191960; h=Received:DKIM-Signature:Received:Date:Message-ID:From:To:Cc:Subject: In-Reply-To:References:User-Agent:MIME-Version:Content-Type: X-SA-Exim-Connect-IP:X-SA-Exim-Rcpt-To:X-SA-Exim-Mail-From: X-SA-Exim-Scanned; bh=UxofiOisVb0N9dpx3KqX3cKPnOOU4k70NQb6001fjTA=; b=YhxhI5TkODWB949XD+F/6SkJuALtQ2NSnJWnH45g2uhMbOinRAOxNOyPdvCK3/TwgfmJ yA2e7uhTesOSYF/EhnlH0Nnk6+NVtIv4PbpNu1YpTwdRWIZ36Z0jXGBlM2f2u+ZawN+Ie gH2t5GrL0I95lKaqRNepF+o3w+2QM5AI/ka6NAfMl2x1WOatlpQ/Mjn990YIbwV/PiPCG r9FXMAqneQqdcvcw9ZaUkJenOozle+EbA1HX880w1naMKcsE4zj6aiIme/XScQLJQZITi Qis1FwRWHa9H82zJPY9miatO1miV6O1Q/o9BN+hxRk4ZhGk8dqP+Ml5dx3yEakH5xQw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=i+OWXR4l; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B4226606A31C; Wed, 28 Oct 2026 12:52:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=i+OWXR4l Received: by smtp.kernel.org (Postfix) with ESMTPSA id 442AF1F031E0; Wed, 28 Oct 2026 12:52:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793191959; bh=UxofiOisVb0N9dpx3KqX3cKPnOOU4k70NQb6001fjTA=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=i+OWXR4lxfk4bHfMZ5sEYDr5qwuwhsEkYDq5GYE8eLtBQ751L7g+UJ+9oKt3gtt7w 7/Z/9Hzmp/e7bFxSVBfNMUK9zUdCphxlmmFTq3d6GHmj1FnERjGCldQ78VBi6B6h/h wlXWanmG8aBQ1plWgZTM+lJni4pNz+PLpD24AByvlg9TBlZp9QYrwfRsBUqZO5Qyiy raWFVN8CAMdCDoNVVIBPiCBB7xm6gsUl5Cs7WR80QRzUk6JXdjMyQ/9hLKV9AnjYMD Br4am5wJuQ8fb6own0X8Kp99w8H7/lTTCxMxzovCFxDjGMc3tN5IFjVm5tQ1/ooFOF EB0Mxwb2uOO6w== 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 1xM38v-000000087PU-0G2H; Wed, 28 Oct 2026 12:52:37 +0000 Date: Wed, 28 Oct 2026 12:52:36 +0000 Message-ID: <86mrryxa0b.wl-maz@kernel.org> From: Marc Zyngier To: Fuad Tabba Cc: Oliver Upton , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Mark Rutland , Vincent Donnefort , kernel-team@android.com, linux-kernel@vger.kernel.org, Oculytic , Fuad Tabba Subject: Re: [PATCH v2 3/3] KVM: arm64: Disable host PMU counters for protected guests In-Reply-To: <20261028110739.2366566-4-fuad.tabba@linux.dev> References: <20261028110739.2366566-1-fuad.tabba@linux.dev> <20261028110739.2366566-4-fuad.tabba@linux.dev> 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) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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: fuad.tabba@linux.dev, oupton@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, vdonnefort@google.com, kernel-team@android.com, linux-kernel@vger.kernel.org, oculytic@gmail.com, tabba@google.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Wed, 28 Oct 2026 11:07:39 +0000, Fuad Tabba wrote: > > A protected guest has no PMU, and EL2 clears MDCR_EL2.HPME for it. > However, HPME has no effect, since __pkvm_vcpu_load() sets HPMN to cover > every event counter, and HPME never covers the cycle or instruction > counter. The counters the host has enabled therefore keep counting the > guest. > > Stop them in the world switch while a protected guest runs, reading > PMCNTENSET_EL0 rather than trusting the host-controlled events mask. > Gate this on system_supports_pmuv3(), as __activate_traps_common() does > for PMUSERENR_EL0. > > Side channels are outside pKVM's threat model, so this is hardening > rather than a fix. > > Reported-by: Oculytic > Signed-off-by: Fuad Tabba > --- > arch/arm64/kvm/hyp/nvhe/switch.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c > index 91e1edf40bcd2..f602154ab49b5 100644 > --- a/arch/arm64/kvm/hyp/nvhe/switch.c > +++ b/arch/arm64/kvm/hyp/nvhe/switch.c > @@ -175,6 +175,26 @@ static void __pmu_switch_to_host(struct kvm_vcpu *vcpu) > #define __pmu_switch_to_host(v) do {} while (0) > #endif > > +static u64 __pmu_stop_host_counters(struct kvm_vcpu *vcpu) > +{ > + u64 pmcnten; > + > + if (!vcpu_is_protected(vcpu) || !system_supports_pmuv3()) > + return 0; > + > + pmcnten = read_sysreg(pmcntenset_el0); > + if (pmcnten) > + write_sysreg(pmcnten, pmcntenclr_el0); It feels a bit odd to change the individual counter enables, rather than just use PMCR_EL0.E, which is designed for this purpose. It probably doesn't change much, but it'd certainly make the intent a bit more obvious. Or am I missing something? Thanks, M. -- Without deviation from the norm, progress is not possible.