From mboxrd@z Thu Jan 1 00:00:00 1970 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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 34D79C43458 for ; Tue, 14 Jul 2026 09:17:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:Message-ID:Date:Subject:Cc:To:From:Reply-To:Content-Type: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Owner; bh=SMpdyicM6ZYlIk0X2zXglwqGKrp0spNpaPbbnN9IPcs=; b=Zk3YKelR3qNKLksxnrUtqOWJpY 7rAtLCU1QPhzVm9XjRAGnmJbKEZ6ZV42z3vqx4IxScLSw/7NkW+375SeTXKM1BLRCqaEp+ZBNtEOA DnViZqPnfWSTATm8rbrHD/IAUl0slkf5vvsUzf4o2gYqdsK5cFSJrlsL0F/sj9PTrfyVcd+5t4M2Q TkNBDbVAYFDLu5ly8ymoM03r55Zoo3uE22iM+lBdXma+kFENQLQSVPzKc4H9x4Y9nvPAkNftCYJ2E T6LFbz5ibwZZVh58XakmtOB7kscgpeLPYjVWog0oAVhg/Bn6ajqN0QwHmXuPUZL0vhtlaGYj/pGdW eaZRJ4lQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wjZFy-0000000BP1N-13xc; Tue, 14 Jul 2026 09:16:50 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wjZFx-0000000BP0u-1c1p for linux-arm-kernel@lists.infradead.org; Tue, 14 Jul 2026 09:16:49 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 14EDA408B6; Tue, 14 Jul 2026 09:16:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EC0661F000E9; Tue, 14 Jul 2026 09:16:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784020609; bh=SMpdyicM6ZYlIk0X2zXglwqGKrp0spNpaPbbnN9IPcs=; h=From:To:Cc:Subject:Date; b=MGWdd89U/byRf8tLD6L2CVTs5dmwutok7Ws9zE+zcWq3HBNnySERzFhrK5flki7rM WOijEy97y1K3GP97a3Hdb11g2IWC6Sg/wt2mFBKaiJvbn69NR63P+emSqfXjKwIQhz zNjsiBZBDr8NxFlCLN5v8TurXVeoOl0yc9I6zbHdOXX1voHTbMsBxRMdR13VBD0HcL XIxKDGhk7WOiMEFQuIDZGw3A7PPDqFhr2jswBTlh0WyL5I2jnBYgDUO8DTRjViPB8S Qs77hcGgWpKtdzpNVXMqzHcb79bX51Ei0ZgrGlU6bOYUXRMSNdzRc8g8n4UiVLWFHT L3IHaurpwxVxg== Received: from sofa.misterjones.org ([185.219.108.64] helo=valley-girl.lan) 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 1wjZFu-00000004ny1-3uJc; Tue, 14 Jul 2026 09:16:47 +0000 From: Marc Zyngier To: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org Cc: Steffen Eiden , Joey Gouly , Suzuki K Poulose , Oliver Upton , Zenghui Yu Subject: [PATCH v2 00/28] KVM: arm64: Add support for FEAT_NV2p1 and FEAT_NV3 Date: Tue, 14 Jul 2026 10:16:13 +0100 Message-ID: <20260714091641.1970822-1-maz@kernel.org> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, seiden@linux.ibm.com, joey.gouly@arm.com, suzuki.poulose@arm.com, oupton@kernel.org, yuzenghui@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false 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 This is the second version of a series adding support for two extensions targeting Nested Virt on arm64: - FEAT_NV2p1 is effectively a bug fix for two registers (CNTHCTL_EL2 and CPTR_EL2) that are missing stateful bits when accessed from EL1 in a NV configuration. When this is present, the hypervisor can avoid a bunch of traps. - FEAT_NV3 is much more ambitious, and changes the way ERET behaves in a NV environment. By moving EL1 accesses to HCR_EL2 from memory (via VNCR) to a dedicated register (NVHCR_EL2), the HW can detect whether the guest is performing an ERET for itself (NVHCR_EL2.TGE==1) or to its own guest (NVHCR_EL2.TGE==0). In the former case, ERET is done directly, and no trap occurs. Similar optimisations are available for a class of TLBI instructions. The whole thing has been tested on an FVP model, and shown measurable improvements for an L1 guest (about 1.5% fewer instructions). Given that this isn't very convincing on its own, I have built an approximate emulation of FEAT_NV3 that L1 (and deeper levels) can use on actual production hardware. For these deeper levels, the numbers are in the double digit of percentage point reduction, see below for details. Does it make NV better? Yes! Does it make NV good? Get real! Anyway, patches on top of -rc3 plus the current state of kvmarm/fixes. * Side notes about performance evaluation with NV3 emulation: If you are interested in the NV3 emulation, I have a branch [0] that contains it all. Note that the improvement only kicks while running an L2 guest running at EL2 -- L1 will not see any improvement. But I get close to 40% improvements on L2, and 60% on L3 for the only workload that really matters (Debian Installer). If all your nested guests are running this hack, then you can pass "kvm-arm.mode=nested,nvtge" on the host command line, and all the nested guests will opt in the accelerated behaviour. If you like to live dangerously (or have a machine that does not have FEAT_HCX), you can instead pass 'kvm-arm.mode=nested,nvtge=force', and ERET will get the acceleration without even guest buy-in. * From v1 [1]: - Expanded generation of RESx and UNKN symbols to both Mapping and Fields qualifiers - Dropped HFGIRT_EL2.ERET checks on ERET fast-path - Fixed the NVHCR_EL2 trap handling - Added FORCE_RESx() to HCRX_EL2 constraints - Fixed ID_AA64MMFR4_EL1 sanitisation - Added NV3 acceleration for TLBIOS - Collected RBs from Joey, with thanks [0] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/nv3 [1] https://lore.kernel.org/r/20260702160248.1377250-1-maz@kernel.org Marc Zyngier (28): arm64: sysreg: Emit RESx/UNKN values for Mapping/Fields definitions arm64: Update ID_AA64MMFR4_EL1 description to 2026-03 JSON release KVM: arm64: Merge guest's HCRX_EL2 using NV_HCRX_GUEST_EXCLUDE KVM: arm64: Drop __HCRX_EL2_* masks KVM: arm64: Plumb HCRX_EL2.SRMASKEn in HCRX_EL2 sanitisation KVM: arm64: Classify CPTR_EL2 as a SR_LOC_SPECIAL register KVM: arm64: Don't evaluate HCR_EL2.NV nor HFGITR_EL2.ERET on ERET fast path arm64: Add ARM64_HAS_NV2P1 capability KVM: arm64: Relax CPTR_EL2 handling when FEAT_NV2p1 is present KVM: arm64: Relax CNTHCTL_EL2 handling when FEAT_NV2p1 is present KVM: arm64: Expose FEAT_NV2p1 to NV guests arm64: Add FEAT_NV2p1 detection arm64: sysreg: Add NVHCR_EL2 description as a mirror of HCR_EL2 arm64: sysreg: Add HCRX_EL2 bits related to FEAT_NV3 arm64: Add ARM64_HAS_NV3 capability KVM: arm64: Split NV-specific exit fixups from the non-NV handling KVM: arm64: Add NV3 control bits to HCRX_EL2 sanitisation KVM: arm64: Add kvm_has_nv{2,3}() predicates KVM: arm64: Make HCR_EL2 a non-VNCR register KVM: arm64: Add sanitisation for NVHCR_EL2 KVM: arm64: Add NVHCR_EL2 handling to the sysreg array KVM: arm64: Add routing for NVHCR_EL2 trap KVM: arm64: Add NVHCR_EL2 context switching KVM: arm64: Engage NV3 ERET trap elision KVM: arm64: Engage NV3 TLBI trap elision KVM: arm64: Add FEAT_NV3 detection KVM: arm64: Expose FEAT_NV3 to guests arm64: Add override for ID_AA64MMFR4_EL1.NV_frac arch/arm64/include/asm/cpufeature.h | 1 + arch/arm64/include/asm/kvm_arm.h | 15 ------ arch/arm64/include/asm/kvm_emulate.h | 45 ++++++++++++++++- arch/arm64/include/asm/kvm_host.h | 3 +- arch/arm64/include/asm/vncr_mapping.h | 2 +- arch/arm64/kernel/cpufeature.c | 18 ++++++- arch/arm64/kernel/image-vars.h | 1 + arch/arm64/kernel/pi/idreg-override.c | 10 ++++ arch/arm64/kvm/arch_timer.c | 10 +++- arch/arm64/kvm/config.c | 27 +++++++++- arch/arm64/kvm/emulate-nested.c | 18 +++++-- arch/arm64/kvm/hyp/include/hyp/switch.h | 27 ++++++++-- arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 11 +++++ arch/arm64/kvm/hyp/vhe/switch.c | 49 ++++++++++++++----- arch/arm64/kvm/hyp/vhe/sysreg-sr.c | 21 +++++--- arch/arm64/kvm/nested.c | 14 +++++- arch/arm64/kvm/sys_regs.c | 57 ++++++++++++++++++++-- arch/arm64/tools/cpucaps | 2 + arch/arm64/tools/gen-sysreg.awk | 8 +-- arch/arm64/tools/sysreg | 42 ++++++++++++++-- 20 files changed, 316 insertions(+), 65 deletions(-) -- 2.47.3