From patchwork Thu Oct 28 11:16:36 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Zyngier X-Patchwork-Id: 12589883 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0430CC433EF for ; Thu, 28 Oct 2021 11:18:11 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B717F60FF2 for ; Thu, 28 Oct 2021 11:18:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org B717F60FF2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=zJqNQryg7l7dkud5T8wRvTdxmQevYpWDyUeyeaLGmTQ=; b=BdX36jKdFFtL52 rVbMnmFMVhsHmW7VANfG3lj1r0I9Cq6OkV4yAvWKb/vK4UGY9tS3G8zK4YXscxVUKYhrDD8zUjw+C cErFA+wEuQnjNbgfD0olr1v/pXL1c2qT2koilpJNIr9k5SL8AxTqGMdCl4VT0hnV1qMdlLGqMZJZ4 UUjkbcwyy9eXUBqbuWw99VvyVtr6fcV/FMTFCrQ8r+aV3ISlmPYnklL0VvMIo/+IO8pYm9ElI3MKU +o/7slw9iDPjhsztwUb9CgrfcEncVi8A7DeNGFqXWp2bLX9x3xwoQ+yarQkLSX22W8ISRPkT+6czC A7E5B4jWGInAIeK4CxyQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3Os-007eGq-JK; Thu, 28 Oct 2021 11:16:50 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3Oo-007eEc-Kc for linux-arm-kernel@lists.infradead.org; Thu, 28 Oct 2021 11:16:47 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D9E1C61106; Thu, 28 Oct 2021 11:16:45 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.lan) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mg3Ol-002BtD-VA; Thu, 28 Oct 2021 12:16:44 +0100 From: Marc Zyngier To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: James Morse , Suzuki K Poulose , Alexandru Elisei , Quentin Perret , Will Deacon , broonie@kernel.org, kernel-team@android.com Subject: [PATCH v2 1/5] KVM: arm64: Reorder vcpu flag definitions Date: Thu, 28 Oct 2021 12:16:36 +0100 Message-Id: <20211028111640.3663631-2-maz@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20211028111640.3663631-1-maz@kernel.org> References: <20211028111640.3663631-1-maz@kernel.org> MIME-Version: 1.0 X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, james.morse@arm.com, suzuki.poulose@arm.com, alexandru.elisei@arm.com, qperret@google.com, will@kernel.org, broonie@kernel.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211028_041646_722978_9D6BA69C X-CRM114-Status: GOOD ( 14.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org The vcpu arch flags are in an interesting, semi random order. As I have made the mistake of reusing a flag once, let's rework this in an order that I find a bit less confusing. Signed-off-by: Marc Zyngier --- arch/arm64/include/asm/kvm_host.h | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index f8be56d5342b..1363c1ff66fb 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -416,14 +416,12 @@ struct kvm_vcpu_arch { #define KVM_ARM64_VCPU_SVE_FINALIZED (1 << 6) /* SVE config completed */ #define KVM_ARM64_GUEST_HAS_PTRAUTH (1 << 7) /* PTRAUTH exposed to guest */ #define KVM_ARM64_PENDING_EXCEPTION (1 << 8) /* Exception pending */ +/* + * Overlaps with KVM_ARM64_EXCEPT_MASK on purpose so that it can't be + * set together with an exception... + */ +#define KVM_ARM64_INCREMENT_PC (1 << 9) /* Increment PC */ #define KVM_ARM64_EXCEPT_MASK (7 << 9) /* Target EL/MODE */ -#define KVM_ARM64_DEBUG_STATE_SAVE_SPE (1 << 12) /* Save SPE context if active */ -#define KVM_ARM64_DEBUG_STATE_SAVE_TRBE (1 << 13) /* Save TRBE context if active */ - -#define KVM_GUESTDBG_VALID_MASK (KVM_GUESTDBG_ENABLE | \ - KVM_GUESTDBG_USE_SW_BP | \ - KVM_GUESTDBG_USE_HW | \ - KVM_GUESTDBG_SINGLESTEP) /* * When KVM_ARM64_PENDING_EXCEPTION is set, KVM_ARM64_EXCEPT_MASK can * take the following values: @@ -441,11 +439,13 @@ struct kvm_vcpu_arch { #define KVM_ARM64_EXCEPT_AA64_EL1 (0 << 11) #define KVM_ARM64_EXCEPT_AA64_EL2 (1 << 11) -/* - * Overlaps with KVM_ARM64_EXCEPT_MASK on purpose so that it can't be - * set together with an exception... - */ -#define KVM_ARM64_INCREMENT_PC (1 << 9) /* Increment PC */ +#define KVM_ARM64_DEBUG_STATE_SAVE_SPE (1 << 12) /* Save SPE context if active */ +#define KVM_ARM64_DEBUG_STATE_SAVE_TRBE (1 << 13) /* Save TRBE context if active */ + +#define KVM_GUESTDBG_VALID_MASK (KVM_GUESTDBG_ENABLE | \ + KVM_GUESTDBG_USE_SW_BP | \ + KVM_GUESTDBG_USE_HW | \ + KVM_GUESTDBG_SINGLESTEP) #define vcpu_has_sve(vcpu) (system_supports_sve() && \ ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE)) From patchwork Thu Oct 28 11:16:37 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Zyngier X-Patchwork-Id: 12589889 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2BBA0C433EF for ; Thu, 28 Oct 2021 11:18:48 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id F006360230 for ; Thu, 28 Oct 2021 11:18:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org F006360230 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=/fI9BfStDpOW/I4DuehQWTkFFZqWakOyvW54liLOLkM=; b=lRqILAajzaIfpl N17wT8vfl93Cc6H3xQuefDnrHZqpYMk4BR9ZUIQyg8dAibwUIjrOqnq6rjatixVgFdxeh3puOjtJc 6LHQ47IQs7VScKU7/jqgrfG7727xhNSUuFsUNivOMZ2Ls5YsGzkF7WNV0mqstAvFlingrkgYYrs3p KsiBl9nPZzJX3cr1lnigUzKSy8lKqxl9gVz1Evbo6v1hQr9wlsfJ96pEW7iTIdgbBcGf/4dpNGCWX 2YFdREDdWeW3OyjUXdqGbEuWVGRSDyi1geqY5Pyjvj+SVo/YxnABHSPj+ogilIPNDWTWCtE5/p2af pQEu1tF+ltMwIJryXqUw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3PU-007ePX-QT; Thu, 28 Oct 2021 11:17:28 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3Oo-007eEe-No for linux-arm-kernel@lists.infradead.org; Thu, 28 Oct 2021 11:16:49 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EF9F561107; Thu, 28 Oct 2021 11:16:45 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.lan) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mg3Om-002BtD-6g; Thu, 28 Oct 2021 12:16:44 +0100 From: Marc Zyngier To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: James Morse , Suzuki K Poulose , Alexandru Elisei , Quentin Perret , Will Deacon , broonie@kernel.org, kernel-team@android.com Subject: [PATCH v2 2/5] KVM: arm64: Get rid of host SVE tracking/saving Date: Thu, 28 Oct 2021 12:16:37 +0100 Message-Id: <20211028111640.3663631-3-maz@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20211028111640.3663631-1-maz@kernel.org> References: <20211028111640.3663631-1-maz@kernel.org> MIME-Version: 1.0 X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, james.morse@arm.com, suzuki.poulose@arm.com, alexandru.elisei@arm.com, qperret@google.com, will@kernel.org, broonie@kernel.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211028_041646_878058_2132D3D4 X-CRM114-Status: GOOD ( 22.91 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org The SVE host tracking in KVM is pretty involved. It relies on a set of flags tracking the ownership of the SVE register, as well as that of the EL0 access. It is also pretty scary: __hyp_sve_save_host() computes a thread_struct pointer and obtains a sve_state which gets directly accessed without further ado, even on nVHE. How can this even work? The answer to that is that it doesn't, and that this is mostly dead code. Closer examination shows that on executing a syscall, userspace loses its SVE state entirely. This is part of the ABI. Another thing to notice is that although the kernel provides helpers such as kernel_neon_begin()/end(), they only deal with the FP/NEON state, and not SVE. Given that you can only execute a guest as the result of a syscall, and that the kernel cannot use SVE by itself, it becomes pretty obvious that there is never any host SVE state to save, and that this code is only there to increase confusion. Get rid of the TIF_SVE tracking and host save infrastructure altogether. Signed-off-by: Marc Zyngier Reviewed-by: Mark Brown --- arch/arm64/include/asm/kvm_host.h | 1 - arch/arm64/kvm/fpsimd.c | 17 +++++----------- arch/arm64/kvm/hyp/include/hyp/switch.h | 27 +++---------------------- 3 files changed, 8 insertions(+), 37 deletions(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 1363c1ff66fb..e24d960244d9 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -410,7 +410,6 @@ struct kvm_vcpu_arch { #define KVM_ARM64_DEBUG_DIRTY (1 << 0) #define KVM_ARM64_FP_ENABLED (1 << 1) /* guest FP regs loaded */ #define KVM_ARM64_FP_HOST (1 << 2) /* host FP regs loaded */ -#define KVM_ARM64_HOST_SVE_IN_USE (1 << 3) /* backup for host TIF_SVE */ #define KVM_ARM64_HOST_SVE_ENABLED (1 << 4) /* SVE enabled for EL0 */ #define KVM_ARM64_GUEST_HAS_SVE (1 << 5) /* SVE exposed to guest */ #define KVM_ARM64_VCPU_SVE_FINALIZED (1 << 6) /* SVE config completed */ diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c index 5621020b28de..38ca332c10fe 100644 --- a/arch/arm64/kvm/fpsimd.c +++ b/arch/arm64/kvm/fpsimd.c @@ -73,15 +73,11 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu) void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) { BUG_ON(!current->mm); + BUG_ON(test_thread_flag(TIF_SVE)); - vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED | - KVM_ARM64_HOST_SVE_IN_USE | - KVM_ARM64_HOST_SVE_ENABLED); + vcpu->arch.flags &= ~KVM_ARM64_FP_ENABLED; vcpu->arch.flags |= KVM_ARM64_FP_HOST; - if (test_thread_flag(TIF_SVE)) - vcpu->arch.flags |= KVM_ARM64_HOST_SVE_IN_USE; - if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN) vcpu->arch.flags |= KVM_ARM64_HOST_SVE_ENABLED; } @@ -115,13 +111,11 @@ void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu) void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) { unsigned long flags; - bool host_has_sve = system_supports_sve(); - bool guest_has_sve = vcpu_has_sve(vcpu); local_irq_save(flags); if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) { - if (guest_has_sve) { + if (vcpu_has_sve(vcpu)) { __vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR); /* Restore the VL that was saved when bound to the CPU */ @@ -131,7 +125,7 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) } fpsimd_save_and_flush_cpu_state(); - } else if (has_vhe() && host_has_sve) { + } else if (has_vhe() && system_supports_sve()) { /* * The FPSIMD/SVE state in the CPU has not been touched, and we * have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been @@ -145,8 +139,7 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0); } - update_thread_flag(TIF_SVE, - vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE); + update_thread_flag(TIF_SVE, 0); local_irq_restore(flags); } diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h index a0e78a6027be..722dfde7f1aa 100644 --- a/arch/arm64/kvm/hyp/include/hyp/switch.h +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h @@ -207,16 +207,6 @@ static inline bool __populate_fault_info(struct kvm_vcpu *vcpu) return __get_fault_info(esr, &vcpu->arch.fault); } -static inline void __hyp_sve_save_host(struct kvm_vcpu *vcpu) -{ - struct thread_struct *thread; - - thread = container_of(vcpu->arch.host_fpsimd_state, struct thread_struct, - uw.fpsimd_state); - - __sve_save_state(sve_pffr(thread), &vcpu->arch.host_fpsimd_state->fpsr); -} - static inline void __hyp_sve_restore_guest(struct kvm_vcpu *vcpu) { sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1, SYS_ZCR_EL2); @@ -228,21 +218,14 @@ static inline void __hyp_sve_restore_guest(struct kvm_vcpu *vcpu) /* Check for an FPSIMD/SVE trap and handle as appropriate */ static inline bool __hyp_handle_fpsimd(struct kvm_vcpu *vcpu) { - bool sve_guest, sve_host; + bool sve_guest; u8 esr_ec; u64 reg; if (!system_supports_fpsimd()) return false; - if (system_supports_sve()) { - sve_guest = vcpu_has_sve(vcpu); - sve_host = vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE; - } else { - sve_guest = false; - sve_host = false; - } - + sve_guest = vcpu_has_sve(vcpu); esr_ec = kvm_vcpu_trap_get_class(vcpu); if (esr_ec != ESR_ELx_EC_FP_ASIMD && esr_ec != ESR_ELx_EC_SVE) @@ -269,11 +252,7 @@ static inline bool __hyp_handle_fpsimd(struct kvm_vcpu *vcpu) isb(); if (vcpu->arch.flags & KVM_ARM64_FP_HOST) { - if (sve_host) - __hyp_sve_save_host(vcpu); - else - __fpsimd_save_state(vcpu->arch.host_fpsimd_state); - + __fpsimd_save_state(vcpu->arch.host_fpsimd_state); vcpu->arch.flags &= ~KVM_ARM64_FP_HOST; } From patchwork Thu Oct 28 11:16:38 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Zyngier X-Patchwork-Id: 12589893 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D044C433F5 for ; Thu, 28 Oct 2021 11:19:10 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3208161106 for ; Thu, 28 Oct 2021 11:19:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 3208161106 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=jEisqp+fivPOZ2d/hG0/H6XtW4gzbRZ+klA9UW2J1Sc=; b=Xi+Wp7WDqVDgpB EhBqGdNOCZgWpUVZRvuuauvRV5XNkEJCPJv+4S5q3DSUqeo80jvwqwY4UqRYP7QqsKaUOXzWNWBq7 k3Gd6svvTbz3G6KSQFukXF9yfo0mKa0Qv8YF6lxQiGnGepxc9YDUP5H3rOIWQhO0aCqNPxc54+WKh 0kmvcgpNTCvpV9YY2CWeVrdRoZ0YyS2ZBbJSYE6WiHRqUhGO41p9gLTaFxMnHbrEDxLYmfsVDqsD7 Z49meImaZRfOYfyX+HwOEcjW0AClEw+XEGYADr6I8hLwrSM9D8B/pgiFbt0wjhgcJuR/NE4aJUhyT KXWEdIUzE38FG0Oc5r6w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3Pu-007ebG-PN; Thu, 28 Oct 2021 11:17:54 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3Oo-007eEf-Vy for linux-arm-kernel@lists.infradead.org; Thu, 28 Oct 2021 11:16:49 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4B1736112F; Thu, 28 Oct 2021 11:16:46 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.lan) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mg3Om-002BtD-Gc; Thu, 28 Oct 2021 12:16:44 +0100 From: Marc Zyngier To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: James Morse , Suzuki K Poulose , Alexandru Elisei , Quentin Perret , Will Deacon , broonie@kernel.org, kernel-team@android.com Subject: [PATCH v2 3/5] KVM: arm64: Introduce flag shadowing TIF_FOREIGN_FPSTATE Date: Thu, 28 Oct 2021 12:16:38 +0100 Message-Id: <20211028111640.3663631-4-maz@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20211028111640.3663631-1-maz@kernel.org> References: <20211028111640.3663631-1-maz@kernel.org> MIME-Version: 1.0 X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, james.morse@arm.com, suzuki.poulose@arm.com, alexandru.elisei@arm.com, qperret@google.com, will@kernel.org, broonie@kernel.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211028_041647_089075_5FB64473 X-CRM114-Status: GOOD ( 18.13 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org We currently have to maintain a mapping the thread_info structure at EL2 in order to be able to check the TIF_FOREIGN_FPSTATE flag. In order to eventually get rid of this, start with a vcpu flag that shadows the thread flag on each entry into the hypervisor. Reviewed-by: Mark Brown Signed-off-by: Marc Zyngier --- arch/arm64/include/asm/kvm_host.h | 2 ++ arch/arm64/kvm/arm.c | 1 + arch/arm64/kvm/fpsimd.c | 8 ++++++++ arch/arm64/kvm/hyp/include/hyp/switch.h | 2 +- 4 files changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index e24d960244d9..0db523e447a5 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -440,6 +440,7 @@ struct kvm_vcpu_arch { #define KVM_ARM64_DEBUG_STATE_SAVE_SPE (1 << 12) /* Save SPE context if active */ #define KVM_ARM64_DEBUG_STATE_SAVE_TRBE (1 << 13) /* Save TRBE context if active */ +#define KVM_ARM64_FP_FOREIGN_FPSTATE (1 << 14) #define KVM_GUESTDBG_VALID_MASK (KVM_GUESTDBG_ENABLE | \ KVM_GUESTDBG_USE_SW_BP | \ @@ -735,6 +736,7 @@ long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, /* Guest/host FPSIMD coordination helpers */ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu); void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu); +void kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu *vcpu); void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu); void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu); diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index fe102cd2e518..4afb84e994e2 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -840,6 +840,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) } kvm_arm_setup_debug(vcpu); + kvm_arch_vcpu_ctxflush_fp(vcpu); /************************************************************** * Enter the guest diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c index 38ca332c10fe..f464db2e9e47 100644 --- a/arch/arm64/kvm/fpsimd.c +++ b/arch/arm64/kvm/fpsimd.c @@ -82,6 +82,14 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) vcpu->arch.flags |= KVM_ARM64_HOST_SVE_ENABLED; } +void kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu *vcpu) +{ + if (test_thread_flag(TIF_FOREIGN_FPSTATE)) + vcpu->arch.flags |= KVM_ARM64_FP_FOREIGN_FPSTATE; + else + vcpu->arch.flags &= ~KVM_ARM64_FP_FOREIGN_FPSTATE; +} + /* * If the guest FPSIMD state was loaded, update the host's context * tracking data mark the CPU FPSIMD regs as dirty and belonging to vcpu diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h index 722dfde7f1aa..d49b1b3725f5 100644 --- a/arch/arm64/kvm/hyp/include/hyp/switch.h +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h @@ -44,7 +44,7 @@ static inline bool update_fp_enabled(struct kvm_vcpu *vcpu) * trap the accesses. */ if (!system_supports_fpsimd() || - vcpu->arch.host_thread_info->flags & _TIF_FOREIGN_FPSTATE) + vcpu->arch.flags & KVM_ARM64_FP_FOREIGN_FPSTATE) vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED | KVM_ARM64_FP_HOST); From patchwork Thu Oct 28 11:16:39 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Zyngier X-Patchwork-Id: 12589887 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9C8C5C433EF for ; Thu, 28 Oct 2021 11:18:29 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7003860230 for ; Thu, 28 Oct 2021 11:18:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 7003860230 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Im0+tCsffztKxOU58yY0BRpzCWTuAo/2O6G4ou2spJw=; b=N5DHLKzemio5dB vFxNEWUqNpSUze0giiNGlmCDrgPFQtFx1gmjOecQdHQF9JpHG85HIlnppCNM1GrIemjnnZmvS7kM7 vugW6Y3BxDgB5Fdl6wYSYkQli6Hqi+NL4mIdt62Ycjmt51r4lK48is/iymBbfzThdwFeeXaIP0uzU MIt9zvuwzLiNu2QG7+zcK18shoeEuY7HVyy9A7B5oI292S+hibuVCa09VbHBFzTo1hOsf3fXIwT5K hz8KSiTEkWeBwx8i9VhX1jfDSvsFu2BJLaY1fMUj+ojLObkU6R5jZ4gTHMB+L1VU2y4Y+z0EHx+VV hF3T6CpS52f4TXjvKBdg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3PG-007eLk-W2; Thu, 28 Oct 2021 11:17:15 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3Oo-007eEi-Qp for linux-arm-kernel@lists.infradead.org; Thu, 28 Oct 2021 11:16:49 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 837C361108; Thu, 28 Oct 2021 11:16:46 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.lan) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mg3Om-002BtD-OQ; Thu, 28 Oct 2021 12:16:44 +0100 From: Marc Zyngier To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: James Morse , Suzuki K Poulose , Alexandru Elisei , Quentin Perret , Will Deacon , broonie@kernel.org, kernel-team@android.com Subject: [PATCH v2 4/5] KVM: arm64: Stop mapping current thread_info at EL2 Date: Thu, 28 Oct 2021 12:16:39 +0100 Message-Id: <20211028111640.3663631-5-maz@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20211028111640.3663631-1-maz@kernel.org> References: <20211028111640.3663631-1-maz@kernel.org> MIME-Version: 1.0 X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, james.morse@arm.com, suzuki.poulose@arm.com, alexandru.elisei@arm.com, qperret@google.com, will@kernel.org, broonie@kernel.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211028_041646_935703_84CF9B34 X-CRM114-Status: GOOD ( 17.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Now that we can track an equivalent of TIF_FOREIGN_FPSTATE, drop the mapping of current's thread_info at EL2. Signed-off-by: Marc Zyngier --- arch/arm64/include/asm/kvm_host.h | 2 -- arch/arm64/kvm/fpsimd.c | 12 +----------- arch/arm64/kvm/hyp/include/hyp/switch.h | 1 - arch/arm64/kvm/hyp/nvhe/switch.c | 1 - arch/arm64/kvm/hyp/vhe/switch.c | 1 - 5 files changed, 1 insertion(+), 16 deletions(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 0db523e447a5..da4a82d8ce5d 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -26,7 +26,6 @@ #include #include #include -#include #define __KVM_HAVE_ARCH_INTC_INITIALIZED @@ -320,7 +319,6 @@ struct kvm_vcpu_arch { struct kvm_guest_debug_arch vcpu_debug_state; struct kvm_guest_debug_arch external_debug_state; - struct thread_info *host_thread_info; /* hyp VA */ struct user_fpsimd_state *host_fpsimd_state; /* hyp VA */ struct { diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c index f464db2e9e47..f54d6a1eaff6 100644 --- a/arch/arm64/kvm/fpsimd.c +++ b/arch/arm64/kvm/fpsimd.c @@ -7,7 +7,6 @@ */ #include #include -#include #include #include #include @@ -28,17 +27,9 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu) { int ret; - struct thread_info *ti = ¤t->thread_info; struct user_fpsimd_state *fpsimd = ¤t->thread.uw.fpsimd_state; - /* - * Make sure the host task thread flags and fpsimd state are - * visible to hyp: - */ - ret = create_hyp_mappings(ti, ti + 1, PAGE_HYP); - if (ret) - goto error; - + /* Make sure the host task fpsimd state is visible to hyp: */ ret = create_hyp_mappings(fpsimd, fpsimd + 1, PAGE_HYP); if (ret) goto error; @@ -54,7 +45,6 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu) goto error; } - vcpu->arch.host_thread_info = kern_hyp_va(ti); vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd); error: return ret; diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h index d49b1b3725f5..d2d7b72de84a 100644 --- a/arch/arm64/kvm/hyp/include/hyp/switch.h +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h @@ -28,7 +28,6 @@ #include #include #include -#include extern struct exception_table_entry __start___kvm_ex_table; extern struct exception_table_entry __stop___kvm_ex_table; diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c index a34b01cc8ab9..012890c2af1b 100644 --- a/arch/arm64/kvm/hyp/nvhe/switch.c +++ b/arch/arm64/kvm/hyp/nvhe/switch.c @@ -25,7 +25,6 @@ #include #include #include -#include #include diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c index ded2c66675f0..c7fc04b11673 100644 --- a/arch/arm64/kvm/hyp/vhe/switch.c +++ b/arch/arm64/kvm/hyp/vhe/switch.c @@ -24,7 +24,6 @@ #include #include #include -#include /* VHE specific context */ DEFINE_PER_CPU(struct kvm_host_data, kvm_host_data); From patchwork Thu Oct 28 11:16:40 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Zyngier X-Patchwork-Id: 12589891 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19091C433F5 for ; Thu, 28 Oct 2021 11:18:58 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E1864610FC for ; Thu, 28 Oct 2021 11:18:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org E1864610FC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=cPHQ7vHClWu86LVgepDo55SVLouAi+lbFHaXI897BEE=; b=b00LlCo3ZS9rW9 ZWmSQGdzvMzZNQqOGDwPhfyno3NaEpo8u+DcygvebzlP2GI+LKfzKtDvqJ82OlLHvC+fmxhoK0rXm iCN3aRyHvuezPuGZwUrihEFrxFG3X0T2jzTgVTM8qoiqDCdBvhhfGMXNDao5lslkFBhq6u5onMl8z hWU/N8FGMuSBmawQP352xayZKAOlPeCZI+BI44CajZzWmzAxw7PZetTqvW7DwCnCs8UOzAev81BE4 z/y7viwxaAey5to7SA7gV6CX3xlQhi3QFnchmr9GcuIExzML55dy5U+4mSu5iYTUeq90BdrseW0/P Wt90tBPUvdVHovrS5mxA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3Pg-007eUG-G1; Thu, 28 Oct 2021 11:17:40 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mg3Oq-007eG6-68 for linux-arm-kernel@lists.infradead.org; Thu, 28 Oct 2021 11:16:49 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1089E6112E; Thu, 28 Oct 2021 11:16:47 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.lan) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mg3On-002BtD-6b; Thu, 28 Oct 2021 12:16:45 +0100 From: Marc Zyngier To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: James Morse , Suzuki K Poulose , Alexandru Elisei , Quentin Perret , Will Deacon , broonie@kernel.org, kernel-team@android.com Subject: [PATCH v2 5/5] arm64/fpsimd: Document the use of TIF_FOREIGN_FPSTATE by KVM Date: Thu, 28 Oct 2021 12:16:40 +0100 Message-Id: <20211028111640.3663631-6-maz@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20211028111640.3663631-1-maz@kernel.org> References: <20211028111640.3663631-1-maz@kernel.org> MIME-Version: 1.0 X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, james.morse@arm.com, suzuki.poulose@arm.com, alexandru.elisei@arm.com, qperret@google.com, will@kernel.org, broonie@kernel.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211028_041648_285484_0D733CFD X-CRM114-Status: GOOD ( 15.31 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org The bit of documentation that talks about TIF_FOREIGN_FPSTATE does not mention the ungodly tricks that KVM plays with this flag. Try and document this for the posterity. Signed-off-by: Marc Zyngier --- arch/arm64/kernel/fpsimd.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index ff4962750b3d..1fbd6ba7dbac 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -78,7 +78,11 @@ * indicate whether or not the userland FPSIMD state of the current task is * present in the registers. The flag is set unless the FPSIMD registers of this * CPU currently contain the most recent userland FPSIMD state of the current - * task. + * task. If the task is behaving as a VMM, then this is will be managed by + * KVM which will clear it to indicate that the vcpu FPSIMD state is currently + * loaded on the CPU, allowing the state to be saved if a FPSIMD-aware + * softirq kicks in. Upon vcpu_put(), KVM will save the vcpu FP state and + * flag the register state as invalid. * * In order to allow softirq handlers to use FPSIMD, kernel_neon_begin() may * save the task's FPSIMD context back to task_struct from softirq context.