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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19017C433F5 for ; Fri, 4 Feb 2022 12:05:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241755AbiBDMFN (ORCPT ); Fri, 4 Feb 2022 07:05:13 -0500 Received: from foss.arm.com ([217.140.110.172]:39618 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230211AbiBDMFM (ORCPT ); Fri, 4 Feb 2022 07:05:12 -0500 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 1F15E1480; Fri, 4 Feb 2022 04:05:12 -0800 (PST) Received: from monolith.localdoman (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 54DDC3F40C; Fri, 4 Feb 2022 04:05:09 -0800 (PST) Date: Fri, 4 Feb 2022 12:05:19 +0000 From: Alexandru Elisei To: Marc Zyngier Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Andre Przywara , Christoffer Dall , Jintack Lim , Haibo Xu , Ganapatrao Kulkarni , Chase Conklin , "Russell King (Oracle)" , James Morse , Suzuki K Poulose , karl.heubaum@oracle.com, mihai.carabas@oracle.com, miguel.luis@oracle.com, kernel-team@android.com Subject: Re: [PATCH v6 12/64] KVM: arm64: nv: Add non-VHE-EL2->EL1 translation helpers Message-ID: References: <20220128121912.509006-1-maz@kernel.org> <20220128121912.509006-13-maz@kernel.org> <87fsoz3iti.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87fsoz3iti.wl-maz@kernel.org> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hi Marc, On Thu, Feb 03, 2022 at 06:29:13PM +0000, Marc Zyngier wrote: > On Wed, 02 Feb 2022 17:08:26 +0000, > Alexandru Elisei wrote: > > > > Hi Marc, > > > > On Fri, Jan 28, 2022 at 12:18:20PM +0000, Marc Zyngier wrote: > > > Some EL2 system registers immediately affect the current execution > > > of the system, so we need to use their respective EL1 counterparts. > > > For this we need to define a mapping between the two. In general, > > > this only affects non-VHE guest hypervisors, as VHE system registers > > > are compatible with the EL1 counterparts. > > > > > > These helpers will get used in subsequent patches. > > > > > > Co-developed-by: Andre Przywara > > > Signed-off-by: Andre Przywara > > > Signed-off-by: Marc Zyngier > > > --- > > > arch/arm64/include/asm/kvm_nested.h | 54 +++++++++++++++++++++++++++++ > > > 1 file changed, 54 insertions(+) > > > > > > diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h > > > index fd601ea68d13..5a85be6d8eb3 100644 > > > --- a/arch/arm64/include/asm/kvm_nested.h > > > +++ b/arch/arm64/include/asm/kvm_nested.h > > > @@ -2,6 +2,7 @@ > > > #ifndef __ARM64_KVM_NESTED_H > > > #define __ARM64_KVM_NESTED_H > > > > > > +#include > > > #include > > > > > > static inline bool vcpu_has_nv(const struct kvm_vcpu *vcpu) > > > @@ -11,4 +12,57 @@ static inline bool vcpu_has_nv(const struct kvm_vcpu *vcpu) > > > test_bit(KVM_ARM_VCPU_HAS_EL2, vcpu->arch.features)); > > > } > > > > > > +/* Translation helpers from non-VHE EL2 to EL1 */ > > > +static inline u64 tcr_el2_ps_to_tcr_el1_ips(u64 tcr_el2) > > > +{ > > > + return (u64)FIELD_GET(TCR_EL2_PS_MASK, tcr_el2) << TCR_IPS_SHIFT; > > > +} > > > + > > > +static inline u64 translate_tcr_el2_to_tcr_el1(u64 tcr) > > > +{ > > > + return TCR_EPD1_MASK | /* disable TTBR1_EL1 */ > > > + ((tcr & TCR_EL2_TBI) ? TCR_TBI0 : 0) | > > > + tcr_el2_ps_to_tcr_el1_ips(tcr) | > > > + (tcr & TCR_EL2_TG0_MASK) | > > > + (tcr & TCR_EL2_ORGN0_MASK) | > > > + (tcr & TCR_EL2_IRGN0_MASK) | > > > + (tcr & TCR_EL2_T0SZ_MASK); > > > +} > > > + > > > +static inline u64 translate_cptr_el2_to_cpacr_el1(u64 cptr_el2) > > > +{ > > > + u64 cpacr_el1 = 0; > > > + > > > + if (cptr_el2 & CPTR_EL2_TTA) > > > + cpacr_el1 |= CPACR_EL1_TTA; > > > + if (!(cptr_el2 & CPTR_EL2_TFP)) > > > + cpacr_el1 |= CPACR_EL1_FPEN; > > > + if (!(cptr_el2 & CPTR_EL2_TZ)) > > > + cpacr_el1 |= CPACR_EL1_ZEN; > > > + > > > + return cpacr_el1; > > > +} > > > + > > > +static inline u64 translate_sctlr_el2_to_sctlr_el1(u64 val) > > > +{ > > > + /* Only preserve the minimal set of bits we support */ > > > + val &= (SCTLR_ELx_M | SCTLR_ELx_A | SCTLR_ELx_C | SCTLR_ELx_SA | > > > + SCTLR_ELx_I | SCTLR_ELx_IESB | SCTLR_ELx_WXN | SCTLR_ELx_EE); > > > > Checked that the bit positions are the same between SCTLR_EL2 and SCTLR_EL1. I > > think the IESB bit (bit 21) should be after the WXN bit (bit 19) to be > > consistent; doesn't really matter either way. > > > > > + val |= SCTLR_EL1_RES1; > > > + > > > + return val; > > > +} > > > + > > > +static inline u64 translate_ttbr0_el2_to_ttbr0_el1(u64 ttbr0) > > > +{ > > > + /* Clear the ASID field */ > > > + return ttbr0 & ~GENMASK_ULL(63, 48); > > > +} > > > + > > > +static inline u64 translate_cnthctl_el2_to_cntkctl_el1(u64 cnthctl) > > > +{ > > > + return ((FIELD_GET(CNTHCTL_EL1PCTEN | CNTHCTL_EL1PCEN, cnthctl) << 10) | > > > + (cnthctl & (CNTHCTL_EVNTI | CNTHCTL_EVNTDIR | CNTHCTL_EVNTEN))); > > > > I asked about the field positions in the previous series and this is what you > > replied: > > > > > It's a classic one. Remember that we are running VHE, and remapping a > > > nVHE view of CNTHCTL_EL2 into the VHE view *for the guest*, and that > > > these things are completely shifted around (it has the CNTKCTL_EL1 > > > format). > > > > > > For example, on nVHE, CNTHCTL_EL2.EL1PCTEN is bit 0. On nVHE, this is > > > bit 10. That's why we have this shift, and that you now need some > > > paracetamol. > > > > > > You can also look at the way we deal with the same stuff in > > > kvm_timer_init_vhe()". > > > > Here's how this function is used in vhe/sysreg-sr.c: > > > > static void __sysreg_restore_vel2_state(struct kvm_cpu_context *ctxt) > > { > > [..] > > if (__vcpu_el2_e2h_is_set(ctxt)) { > > [..] > > } else { > > [..] > > val = translate_cnthctl_el2_to_cntkctl_el1(ctxt_sys_reg(ctxt, CNTHCTL_EL2)); > > write_sysreg_el1(val, SYS_CNTKCTL); > > } > > [..] > > } > > > > CNTHCTL_EL2 is a pure EL2 register. The translate function is called > > when guest HCR_EL2.E2H is not set, therefore virtual CNTHCTL_EL2 has > > the non-VHE format. And the result of the function is used to write > > to the hardware CNTKCTL_EL1 register (using the CNTKCTL_EL12 > > encoding), which is different from the CNTHCTL_EL2 > > register. CNTKCTL_EL1 also always has the same format regardless of > > the value of the HCR_EL2.E2H bit. > > > > I don't understand what the host running with VHE has to do with the > > translate function. > > It's just that I completely misunderstood your question, and that I > also failed to realise that this code is just plain buggy. Apologies > for wasting your time on this. > > As it turns out, CNTHCTL_EL2 has *zero* influence on the hypervisor > itself, so messing with it and trying to restore it into CNTKCTL_EL12 > is remarkably pointless. It is solely designed to influence the > execution of EL1. Duh. Hmm... it looks to me like the EVENTI and EVENTDIR fields in CNTHCTL_EL2 do have an effect on the hypervisor. Unfortunately, the control the generation of events from the *physical* counter, while the fields EVENTI and EVENTDIR from CNTKCTL_EL1 control the generation of events from the the *virtual* counter. KVM cannot program CNTKCTL_EL1 to get the same effect as what the L1 hypervisor intended by programming CNTHCTL_EL2, so I think it must program the corresponding physical CNTHCTL_EL2 fields when running the L1 guest. Thoughts? Thanks, Alex > > What it should do is to restore parts of this register *on the host* > so that L1's EL1 is actually influenced by what L1's EL2 has set up > (mostly to handle traps from EL1 to EL2). > > To summarise: > > - the name of the function is misleading: it should be something like > 'translate_nvhe_cnthctl_el2_to_vhe()'. The function is otherwise > correct, and why I was rambling about the bit offsets. > > - the location of the save/restore is wrong: it should happen when > dealing with EL1 instead of EL2 > > - the register it targets is wrong: it should target CNTHTL_EL2 (or > CNTKCTL_EL1 as seen from VHE EL2) > > I'll stick a brown paper bag on my head and wear it for the evening. > > Thanks, > > M. > > -- > Without deviation from the norm, progress is not possible.