From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id E499F436370 for ; Wed, 8 Jul 2026 11:18:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783509522; cv=none; b=CJVnZdkraoeR/Y15fopb9wxyIxRsM5oA+iKkuNzhmo0Qq6fbzee+/BNGNWnxSugVMPmnfrRQSOZWHJo1Vt4sQ+ciOOP86Nlxxe3gv7rRQbafpjwMgUMf5qnh9gM71+H3YVBmgOVbmvzhXJLjBCU012ZV1/eKdfYYF2E1p4e23H0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783509522; c=relaxed/simple; bh=Q3mIYycQy8bOLg/worl5ZK/PQN7XNptnDVDQhCRzReM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Yix1TSyjHweSIOcH9oMlDttaCTX+9Ngf9Y2JSJ8KyyiOY5sgJ2fUDVM8FBWq07EXkNvtzvedMi6SJFcMUWuUHeAB+dzpffahXjHMk6q/IZ3Xr14pyzK6NJTQ0Pb1AiN4zTX4C3oNWuIW+w2ds4W5xqJ1xtpOITOUebyN6+UHOk4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=X9En1xPY; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="X9En1xPY" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A96B71516; Wed, 8 Jul 2026 04:18:34 -0700 (PDT) Received: from e124191.cambridge.arm.com (e124191.cambridge.arm.com [10.2.213.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8BAA73F85F; Wed, 8 Jul 2026 04:18:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1783509519; bh=Q3mIYycQy8bOLg/worl5ZK/PQN7XNptnDVDQhCRzReM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=X9En1xPYusv8IDZUhoObjF477Iwi+uP/2tcsxErNG3U1j4VAUJ3/e3FZ16l4tSQ43 Jkvjm9GWmNxtp09fyP2qj3CQ0aKO/sEr2f2AjcjTcFwgRkRn3UUW4cvnY6Vj1yfhtn L7fOug012cdLeudm56L6DVc3F+m2flj3MBom21pg= Date: Wed, 8 Jul 2026 12:18:32 +0100 From: Joey Gouly To: Marc Zyngier Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, Steffen Eiden , Suzuki K Poulose , Oliver Upton , Zenghui Yu Subject: Re: [PATCH 19/28] KVM: arm64: Make HCR_EL2 a non-VNCR register Message-ID: <20260708111832.GA99849@e124191.cambridge.arm.com> References: <20260702160248.1377250-1-maz@kernel.org> <20260702160248.1377250-20-maz@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260702160248.1377250-20-maz@kernel.org> On Thu, Jul 02, 2026 at 05:02:39PM +0100, Marc Zyngier wrote: > FEAT_NV3 makes a fundamental change to the architecture, by moving > guest-initiated HCR_EL2 accesses to the NVHCR_EL2 register. As the > names suggests, this is HCR_EL2 for a NV guest. > > But where do NVHCR_EL2 accesses from a guest go? The are redirected > to the VNCR page, right where HCR_EL2 is stored in the NV2 case. > Does it hurt? Good. There's more coming. > > The challenge here is to make KVM work seamlessly, without rewriting > everything. Which implies that things such as __vcpu_sys_reg(HCR_EL2) > must work, no matter the underlying NV implementation. > > A simple way to deal with it is to move HCR_EL2's canonical storage > outside of VNCR for the vast majority of the KVM code, and only have > a copy at entry/exit times. Given that we don't really support NV3 > yet, this is pretty simple. > > In the process, advertise NVHCR_EL2 as the register that now holds > offset 0x78 in the VNCR page. > > Signed-off-by: Marc Zyngier Reviewed-by: Joey Gouly > --- > arch/arm64/include/asm/kvm_host.h | 3 ++- > arch/arm64/include/asm/vncr_mapping.h | 2 +- > arch/arm64/kvm/hyp/vhe/switch.c | 9 +++++++++ > 3 files changed, 12 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index bae2c4f92ef5c..2648c8a717ba0 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -543,6 +543,7 @@ enum vcpu_sysreg { > MDCR_EL2, /* Monitor Debug Configuration Register (EL2) */ > CNTHCTL_EL2, /* Counter-timer Hypervisor Control register */ > ZCR_EL2, /* SVE Control Register (EL2) */ > + HCR_EL2, /* Hypervisor Control Register */ > > /* Any VNCR-capable reg goes after this point */ > MARKER(__VNCR_START__), > @@ -571,7 +572,7 @@ enum vcpu_sysreg { > VNCR(TFSR_EL1), /* Tag Fault Status Register (EL1) */ > VNCR(VPIDR_EL2),/* Virtualization Processor ID Register */ > VNCR(VMPIDR_EL2),/* Virtualization Multiprocessor ID Register */ > - VNCR(HCR_EL2), /* Hypervisor Configuration Register */ > + VNCR(NVHCR_EL2),/* NV Hypervisor Configuration Register */ > VNCR(HSTR_EL2), /* Hypervisor System Trap Register */ > VNCR(VTTBR_EL2),/* Virtualization Translation Table Base Register */ > VNCR(VTCR_EL2), /* Virtualization Translation Control Register */ > diff --git a/arch/arm64/include/asm/vncr_mapping.h b/arch/arm64/include/asm/vncr_mapping.h > index 14366d35ce82f..9e8a49fa8b638 100644 > --- a/arch/arm64/include/asm/vncr_mapping.h > +++ b/arch/arm64/include/asm/vncr_mapping.h > @@ -11,7 +11,7 @@ > #define VNCR_VTCR_EL2 0x040 > #define VNCR_VMPIDR_EL2 0x050 > #define VNCR_CNTVOFF_EL2 0x060 > -#define VNCR_HCR_EL2 0x078 > +#define VNCR_NVHCR_EL2 0x078 > #define VNCR_HSTR_EL2 0x080 > #define VNCR_VPIDR_EL2 0x088 > #define VNCR_TPIDR_EL2 0x090 > diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c > index 8268779df4fa9..05bcf8bf7f978 100644 > --- a/arch/arm64/kvm/hyp/vhe/switch.c > +++ b/arch/arm64/kvm/hyp/vhe/switch.c > @@ -70,6 +70,9 @@ static u64 __compute_hcr(struct kvm_vcpu *vcpu) > if (!vcpu_el2_e2h_is_set(vcpu)) > hcr |= HCR_NV1; > > + /* Publish the guest's view of HCR_EL2 to the HW */ > + __vcpu_assign_sys_reg(vcpu, NVHCR_EL2, __vcpu_sys_reg(vcpu, HCR_EL2)); > + > /* > * Nothing in HCR_EL2 should impact running in hypervisor > * context, apart from bits we have defined as RESx (E2H, > @@ -547,6 +550,7 @@ static void fixup_nv_guest_exit(struct kvm_vcpu *vcpu) > */ > if (unlikely(host_data_test_flag(VCPU_IN_HYP_CONTEXT))) { > u64 mode = *vcpu_cpsr(vcpu) & (PSR_MODE_MASK | PSR_MODE32_BIT); > + u64 hcr; > > switch (mode) { > case PSR_MODE_EL1t: > @@ -559,6 +563,11 @@ static void fixup_nv_guest_exit(struct kvm_vcpu *vcpu) > > *vcpu_cpsr(vcpu) &= ~(PSR_MODE_MASK | PSR_MODE32_BIT); > *vcpu_cpsr(vcpu) |= mode; > + > + /* Publish the latest HCR_EL2 to the emulation */ > + hcr = __vcpu_sys_reg(vcpu, NVHCR_EL2); My alarm bells went off reading this, because the context (in-memory) seemed wrong, but I see that patch 23 further modifies this for NV3! > + > + __vcpu_assign_sys_reg(vcpu, HCR_EL2, hcr); > } > > /* Apply extreme paranoia! */ > -- > 2.47.3 >