From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-125.mta1.migadu.com [95.215.58.125]) (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 146B651A140 for ; Thu, 1 Oct 2026 13:59:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.125 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790863161; cv=none; b=icjZw1ekfR7cUahmNyfFIaRVbUOWgXeyYLVtYf2JdfsrxLgXfAmpudHOAr/FJtPlUxkiTPa2K4M9H2GaNPoNPTitVFPEZ1sPb7Yo7cTzAGAKZBVPZazKhqdMxIAiBaUA8b7iqJuNLwY15mXGFV9KO/t+8D3b2ZOF2rhQ7FUGRG8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790863161; c=relaxed/simple; bh=8PgbjM3RudzbwOkoe5Gt2RQoxYVPLiuGki2F4kB8jq4=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=tzbkI5oOo95+xsGATvvi5vKfatvSoDh5lkuBR/nj/c/FlCMdwCAC+RIt8ufh5AoAy9ubNsqkAjKoNDF2j1P8KxdS34ma5tksMM20AT86opiiid3fwJ5JazDDwZi+rhdDkYdh3o+Dyx6K1j3nZ7WZQAwY3iLf0a3o9G9EcxL0aFM= 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=QC9CjX0a; arc=none smtp.client-ip=95.215.58.125 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="QC9CjX0a" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=8PgbjM3RudzbwOkoe5Gt2RQoxYVPLiuGki2F4kB8jq4=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790863158; v=1; x=1791467958; b=QC9CjX0ati5vaQheM/gwz2+H83RSittLuCB2DXPdXAaKPzFDdK3nr/RatpZUKVYd6Mf2DV+7 upNXka0MtzmgAT9LnbGU5IxUMh0+zLjn7OPSg0OuBRvSWlCCRde4cVls932Q5tlyn9Offm8m0TB 9zYzopToVvrQHGoT653/AEh0= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 43ef2dae9eb95ac3; Thu, 01 Oct 2026 13:59:18 +0000 X-Mizu-Trace-ID: 43ef2dae9eb95ac3 X-Migadu-Flow: FLOW_OUT From: Fuad Tabba To: maz@kernel.org, oupton@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: 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: [PATCH v4 16/18] KVM: arm64: Reject host power-on of a vCPU that EL2 holds powered off Date: Thu, 1 Oct 2026 14:57:09 +0100 Message-Id: <20261001135711.1640520-17-fuad.tabba@linux.dev> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20261001135711.1640520-1-fuad.tabba@linux.dev> References: <20261001135711.1640520-1-fuad.tabba@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 A protected vCPU's power state belongs to EL2, which changes it only on the guest's own PSCI calls. KVM_SET_MP_STATE(RUNNABLE) on a vCPU EL2 holds powered off changes the host's copy alone, and the guest's next CPU_ON of that vCPU then fails: mp_state is no longer STOPPED, so the host returns ALREADY_ON, and the guest's retry fails the same way until the VMM stops the vCPU again. SUSPENDED has the same effect. Record a vCPU EL2 holds powered off as KVM_MP_STATE_UNINITIALIZED, an encoding arm64 didn't use: the guest's CPU_OFF writes it, as does hyp vCPU creation for a vCPU that starts STOPPED, and only the guest's CPU_ON writes RUNNABLE over it. RUNNABLE and SUSPENDED from the VMM return -EPERM on it, the VMM can't write the value itself, and KVM_ARM_VCPU_INIT, which would write STOPPED or RUNNABLE over it, is rejected once the vCPU has run. The VMM can still pause and resume a vCPU EL2 has powered on. Neither STOPPED nor kvm_prepare_system_event() overwrites the value: a vCPU at it is already off, and a STOPPED in its place would turn the guest's next CPU_ON into ALREADY_ON, after a SYSTEM_RESET exit the VMM runs on from. kvm_arm_vcpu_stopped() covers it, so the run loop sleeps the vCPU as before. The guest's CPU_ON is gated on the value rather than on STOPPED. A STOPPED written between the target's CPU_OFF exit and the host's power-off of it, which kvm_prepare_system_event() can do from another vCPU's SYSTEM_OFF or SYSTEM_RESET, would otherwise let the CPU_ON through, and the power-off would then record the target powered off while EL2 holds it ON_PENDING, with no way back before VM teardown. Gated on the value, that CPU_ON returns ALREADY_ON and the retry succeeds once the power-off has run. Signed-off-by: Fuad Tabba --- arch/arm64/include/asm/kvm_host.h | 1 + arch/arm64/kvm/arm.c | 35 +++++++++++++++++++++++++------ arch/arm64/kvm/pkvm.c | 21 +++++++++++++++---- arch/arm64/kvm/psci.c | 11 ++++++++-- 4 files changed, 56 insertions(+), 12 deletions(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 37d0721d39a45..e99b706c879cf 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -1564,6 +1564,7 @@ static inline void kvm_hyp_reserve(void) { } void kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu); bool kvm_arm_vcpu_stopped(struct kvm_vcpu *vcpu); +bool kvm_pkvm_vcpu_is_powered_off(struct kvm_vcpu *vcpu); static inline u64 *__vm_id_reg(struct kvm_arch *ka, u32 reg) { diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 14fe4e7275796..a89087c83e27f 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -770,23 +770,28 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) vcpu->cpu = -1; } -static void __kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu) +static void __kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu, u32 mp_state) { - WRITE_ONCE(vcpu->arch.mp_state.mp_state, KVM_MP_STATE_STOPPED); + WRITE_ONCE(vcpu->arch.mp_state.mp_state, mp_state); kvm_make_request(KVM_REQ_SLEEP, vcpu); kvm_vcpu_kick(vcpu); } +/* The guest's own CPU_OFF: EL2 has already powered the vCPU off. */ void kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu) { + u32 mp_state = vcpu_is_protected(vcpu) ? KVM_MP_STATE_UNINITIALIZED : KVM_MP_STATE_STOPPED; + spin_lock(&vcpu->arch.mp_state_lock); - __kvm_arm_vcpu_power_off(vcpu); + __kvm_arm_vcpu_power_off(vcpu, mp_state); spin_unlock(&vcpu->arch.mp_state_lock); } bool kvm_arm_vcpu_stopped(struct kvm_vcpu *vcpu) { - return READ_ONCE(vcpu->arch.mp_state.mp_state) == KVM_MP_STATE_STOPPED; + u32 mp_state = READ_ONCE(vcpu->arch.mp_state.mp_state); + + return mp_state == KVM_MP_STATE_STOPPED || mp_state == KVM_MP_STATE_UNINITIALIZED; } static void kvm_arm_vcpu_suspend(struct kvm_vcpu *vcpu) @@ -801,6 +806,12 @@ static bool kvm_arm_vcpu_suspended(struct kvm_vcpu *vcpu) return READ_ONCE(vcpu->arch.mp_state.mp_state) == KVM_MP_STATE_SUSPENDED; } +/* Only the guest's CPU_ON may start a vCPU EL2 holds powered off. */ +bool kvm_pkvm_vcpu_is_powered_off(struct kvm_vcpu *vcpu) +{ + return READ_ONCE(vcpu->arch.mp_state.mp_state) == KVM_MP_STATE_UNINITIALIZED; +} + int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu, struct kvm_mp_state *mp_state) { @@ -818,12 +829,24 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu, switch (mp_state->mp_state) { case KVM_MP_STATE_RUNNABLE: + if (kvm_pkvm_vcpu_is_powered_off(vcpu)) { + ret = -EPERM; + break; + } + WRITE_ONCE(vcpu->arch.mp_state, *mp_state); break; case KVM_MP_STATE_STOPPED: - __kvm_arm_vcpu_power_off(vcpu); + /* Keep EL2's off record: STOPPED over it would let RUNNABLE through. */ + if (!kvm_pkvm_vcpu_is_powered_off(vcpu)) + __kvm_arm_vcpu_power_off(vcpu, KVM_MP_STATE_STOPPED); break; case KVM_MP_STATE_SUSPENDED: + if (kvm_pkvm_vcpu_is_powered_off(vcpu)) { + ret = -EPERM; + break; + } + kvm_arm_vcpu_suspend(vcpu); break; default: @@ -1788,7 +1811,7 @@ static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu, spin_lock(&vcpu->arch.mp_state_lock); if (power_off) - __kvm_arm_vcpu_power_off(vcpu); + __kvm_arm_vcpu_power_off(vcpu, KVM_MP_STATE_STOPPED); else WRITE_ONCE(vcpu->arch.mp_state.mp_state, KVM_MP_STATE_RUNNABLE); diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c index 8e4c6e4bec123..99a5d9a913129 100644 --- a/arch/arm64/kvm/pkvm.c +++ b/arch/arm64/kvm/pkvm.c @@ -118,12 +118,25 @@ static int __pkvm_create_hyp_vcpu(struct kvm_vcpu *vcpu) return -ENOMEM; ret = kvm_call_hyp_nvhe(__pkvm_init_vcpu, handle, vcpu, hyp_vcpu); - if (!ret) - vcpu_set_flag(vcpu, VCPU_PKVM_FINALIZED); - else + if (ret) { free_pages_exact(hyp_vcpu, hyp_vcpu_sz); + return ret; + } - return ret; + /* + * Mirror EL2's seeding of power_state from mp_state. The hyp vCPU is + * published, so take mp_state_lock against kvm_psci_vcpu_on(). + */ + if (vcpu_is_protected(vcpu)) { + spin_lock(&vcpu->arch.mp_state_lock); + if (kvm_arm_vcpu_stopped(vcpu)) + WRITE_ONCE(vcpu->arch.mp_state.mp_state, KVM_MP_STATE_UNINITIALIZED); + spin_unlock(&vcpu->arch.mp_state_lock); + } + + vcpu_set_flag(vcpu, VCPU_PKVM_FINALIZED); + + return 0; } /* diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c index e3db84400d1f8..b01f8d44033f1 100644 --- a/arch/arm64/kvm/psci.c +++ b/arch/arm64/kvm/psci.c @@ -63,7 +63,12 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu) return PSCI_RET_INVALID_PARAMS; spin_lock(&vcpu->arch.mp_state_lock); - if (!kvm_arm_vcpu_stopped(vcpu)) { + /* + * A protected vCPU is off once the host has acted on EL2's CPU_OFF. + * STOPPED before that is the VMM's pause. + */ + if (!kvm_arm_vcpu_stopped(vcpu) || + (vcpu_is_protected(vcpu) && !kvm_pkvm_vcpu_is_powered_off(vcpu))) { if (kvm_psci_version(source_vcpu) != KVM_ARM_PSCI_0_1) ret = PSCI_RET_ALREADY_ON; else @@ -161,7 +166,9 @@ static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type, u64 flags) */ kvm_for_each_vcpu(i, tmp, vcpu->kvm) { spin_lock(&tmp->arch.mp_state_lock); - WRITE_ONCE(tmp->arch.mp_state.mp_state, KVM_MP_STATE_STOPPED); + /* Keep EL2's off record for the guest's next CPU_ON. */ + if (!kvm_pkvm_vcpu_is_powered_off(tmp)) + WRITE_ONCE(tmp->arch.mp_state.mp_state, KVM_MP_STATE_STOPPED); spin_unlock(&tmp->arch.mp_state_lock); } kvm_make_all_cpus_request(vcpu->kvm, KVM_REQ_SLEEP); -- 2.39.5