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 E27EA46EF64; Mon, 14 Sep 2026 13:42:49 +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=1789393371; cv=none; b=oo2ylPzPu1hrEz1QNk2pRbuS8nl7zaUPC2M+YsuNzVUliUpBSjP11DgTg6Unwzyan04JeuZLV0yO6ZJ60QVGKqL0P25y+walYj1T0f/q4Ga3gYs8NgCi9b8r7YAtSivip88NTAKlx8BAZc48Iwwi3aEreEDm+SfJTdmtLkDjEZo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789393371; c=relaxed/simple; bh=ytG8ocPF34y4GXTp7tqgbP+za6+mvxCiVYZgdi98Zyk=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=SE6pg7W+9IqP1LFu0Gcj40lOnjKvOsC2gQqXbA1VVZmDBDTV38OH77PsAKhlkREY1hDKYVM4aa5ddP4gkDqTZaWYd/Wa1hMtg4GaKSyvgAI6q8HU/4t3WdQ8oWawCG5RvxtSoAA3Pd2+vGky8RTG8orP1wZm81PnpelVs220ixY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=I5tVHzlP; 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="I5tVHzlP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BDA3E1F000FF; Mon, 14 Sep 2026 13:42:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789393369; bh=uXYH+/nJwZIRRlJSJX40vXdbeohaBAmcqYLkggzgf14=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=I5tVHzlPAJ/KrsAxqyGne0O47j8Eak17IwUzmR7gf9kATOVcPOq+QFIGsAXMbBLYa es6/VLTkLxiZublfkTCPl/INOY0TE5ywDyS5quk4ZY+BeVZRLqNBoCllZGAVwA5R/A wDm9GpamkLRxefE9q+BjDQgA3BZjMX5ZM5+KyOvs4Q2Jj+BQ5ifegRcW/tsTZ94EHt 54xVQng6Ayyl06kajswrKHcjWx+U+4UZTRyGtu0wCSIbcFCDcBTibTeNcBvaIU1yyo mHbQU1J7pOwNRUzYn1B9dfdLkgKdXDL2KKDH4vKyezywQ1xRXjew56hpgAeuUq0zHJ lK+nWGAeqloiA== 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 1x66xL-00000008eJ3-3RBw; Mon, 14 Sep 2026 13:42:47 +0000 Date: Mon, 14 Sep 2026 14:42:47 +0100 Message-ID: <8633vc6jag.wl-maz@kernel.org> From: Marc Zyngier To: Fuad Tabba Cc: oupton@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, mark.rutland@arm.com, steven.price@arm.com, vdonnefort@google.com, qperret@google.com, tabba@google.com Subject: Re: [PATCH v3 12/18] KVM: arm64: Prevent host PC adjustments for protected vCPUs In-Reply-To: <20260914113338.159227-13-fuad.tabba@linux.dev> References: <20260914113338.159227-1-fuad.tabba@linux.dev> <20260914113338.159227-13-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) Precedence: bulk X-Mailing-List: linux-kernel@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: fuad.tabba@linux.dev, oupton@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, mark.rutland@arm.com, steven.price@arm.com, vdonnefort@google.com, qperret@google.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 Mon, 14 Sep 2026 12:33:32 +0100, Fuad Tabba wrote: > > __kvm_adjust_pc() lets the host advance a vCPU's PC or inject an > exception, which for a protected vCPU would let the host redirect > guest execution. Drop the request there: the entry handlers apply the > host's PC_UPDATE_REQ on re-entry, where EL2 allows it. > > __kvm_adjust_pc() adjusts the vCPU a get/put pair returns, the one it > was given outside pKVM. Both host callers hold the vCPU mutex, so a > hyp vCPU loaded for the vCPU is loaded on the calling CPU. The request > for a loaded protected vCPU is dropped. For a loaded non-protected > vCPU, PKVM_HOST_STATE_DIRTY selects the copy, since adjusting the hyp > vCPU while the host copy is authoritative loses the update at the next > flush. Adjusting the hyp vCPU copies PC_UPDATE_REQ in and back out > again: without the copy back, INCREMENT_PC outlives the adjustment and > the next KVM_SET_VCPU_EVENTS trips WARN_ON(INCREMENT_PC) in > kvm_pend_exception(). With no hyp vCPU loaded, as under > KVM_SET_VCPU_EVENTS, the host copy is adjusted as before. > > Until the marshalling patch clears PC_UPDATE_REQ on the host copy at > exit, a KVM_RUN that returns to userspace with INCREMENT_PC set leaves > it on the host copy of a loaded protected vCPU, and a > KVM_SET_VCPU_EVENTS before the next run then trips that WARN_ON. > > Suggested-by: Marc Zyngier > Signed-off-by: Fuad Tabba > --- > arch/arm64/kvm/hyp/exception.c | 21 +++++++++----- > arch/arm64/kvm/hyp/include/hyp/adjust_pc.h | 19 +++++++++++++ > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 32 ++++++++++++++++++++++ > 3 files changed, 65 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c > index 6e60d890afa4a..7ea62e5304ae9 100644 > --- a/arch/arm64/kvm/hyp/exception.c > +++ b/arch/arm64/kvm/hyp/exception.c > @@ -353,12 +353,19 @@ static void kvm_inject_exception(struct kvm_vcpu *vcpu) > */ > void __kvm_adjust_pc(struct kvm_vcpu *vcpu) > { > - if (vcpu_get_flag(vcpu, PENDING_EXCEPTION)) { > - kvm_inject_exception(vcpu); > - vcpu_clear_flag(vcpu, PENDING_EXCEPTION); > - vcpu_clear_flag(vcpu, EXCEPT_MASK); > - } else if (vcpu_get_flag(vcpu, INCREMENT_PC)) { > - kvm_skip_instr(vcpu); > - vcpu_clear_flag(vcpu, INCREMENT_PC); > + struct kvm_vcpu *target = pkvm_adjust_pc_get(vcpu); nit: it is really odd to see this 'pkvm' prefix in generic code. The point of it is not only to abstract the pvkm complexity away, but also to have a wrapper that may be of use in other situations. Don't respin the series just for this though, I may end-up changing this when applying it. > + if (!target) > + return; > + I find this one scary, see below. [...] > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index da8ab636063cf..1dcc75261dc08 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -642,6 +642,38 @@ static void handle___pkvm_host_mkyoung_guest(struct kvm_cpu_context *host_ctxt) > cpu_reg(host_ctxt, 1) = ret; > } > > +/* > + * PKVM_HOST_STATE_DIRTY names the authoritative copy, the host's when set. > + * A loaded protected vCPU takes the request at its next entry instead. > + */ > +struct kvm_vcpu *pkvm_adjust_pc_get(struct kvm_vcpu *vcpu) > +{ > + struct pkvm_hyp_vcpu *hyp_vcpu; > + > + if (!is_protected_kvm_enabled()) > + return vcpu; > + > + hyp_vcpu = pkvm_get_loaded_hyp_vcpu(); > + if (!hyp_vcpu || hyp_vcpu->host_vcpu != vcpu) Under which circumstances do we get hyp_vcpu->host_vcpu != vcpu? > + return vcpu; > + > + if (pkvm_hyp_vcpu_is_protected(hyp_vcpu)) > + return NULL; Is it always the case that a protected vcpu cannot see its PC adjusted at all? How is PC updated after an exit for MMIO? I feel there is an interaction with the above, but I'm not 100% certain... > + > + if (vcpu_get_flag(vcpu, PKVM_HOST_STATE_DIRTY)) > + return vcpu; > + > + vcpu_copy_flag(&hyp_vcpu->vcpu, vcpu, PC_UPDATE_REQ); > + return &hyp_vcpu->vcpu; > +} > + > +/* Reflect the consumed request back, otherwise it stays pending. */ > +void pkvm_adjust_pc_put(struct kvm_vcpu *vcpu, struct kvm_vcpu *target) > +{ > + if (target != vcpu) > + vcpu_copy_flag(vcpu, target, PC_UPDATE_REQ); > +} > + > static void handle___kvm_adjust_pc(struct kvm_cpu_context *host_ctxt) > { > DECLARE_REG(struct kvm_vcpu *, vcpu, host_ctxt, 1); Thanks, M. -- Without deviation from the norm, progress is not possible.