From: Kristina Martsenko <kristina.martsenko@arm.com> To: Catalin Marinas <catalin.marinas@arm.com> Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>, Oliver Upton <oliver.upton@linux.dev>, James Morse <james.morse@arm.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Zenghui Yu <yuzenghui@huawei.com>, Mark Rutland <mark.rutland@arm.com>, Mark Brown <broonie@kernel.org>, Luis Machado <luis.machado@arm.com>, Vladimir Murzin <vladimir.murzin@arm.com>, linux-kernel@vger.kernel.org Subject: Re: [PATCH 04/10] arm64: mops: document boot requirements for MOPS Date: Fri, 24 Mar 2023 01:00:43 +0000 [thread overview] Message-ID: <61b0e30a-568c-d7f6-7b67-e9fc8b68de25@arm.com> (raw) In-Reply-To: <ZBSCObGmIXjyeMA6@arm.com> On 17/03/2023 15:07, Catalin Marinas wrote: > On Thu, Feb 16, 2023 at 04:00:06PM +0000, Kristina Martsenko wrote: >> + For CPUs with Memory Copy and Memory Set instructions (FEAT_MOPS): >> + >> + - If the kernel is entered at EL1 and EL2 is present: >> + >> + - HCRX_EL2.MSCEn (bit 11) must be initialised to 0b1. >> + >> + - HCRX_EL2.MCE2 (bit 10) must be initialised to 0b0. > > Regarding MCE2, does EL1 actually care if EL2 wants to handle all the > memcpy/memset exceptions? No, EL1 does not need to handle the exceptions itself, but I don't see any current use case for allowing EL2 to handle it. If it was allowed, I think booting.txt would need to specify exactly what Linux expects EL2 to do if MCE2 is set (eg, that EL2 handles the exception by reformatting registers, modifying single step state, etc). > There may even be a valid case to do this at > EL2 if you run a guest that uses these instructions but has no clue on > how to deal with the specific exception like WrongOption. Not sure I follow - this series adds the exception handling, so how can a Linux guest not know how to handle the exception? Or do you mean that there may be times when EL1 can't take the exception but EL2 may move it to another CPU, and so EL2 would need to handle the exception? I'm not sure if Linux ever uses mops instructions at times like that. Note that this series does not add support for mops in guests yet. I think booting.txt can be updated when that support is added. Thanks, Kristina
WARNING: multiple messages have this Message-ID (diff)
From: Kristina Martsenko <kristina.martsenko@arm.com> To: Catalin Marinas <catalin.marinas@arm.com> Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>, Oliver Upton <oliver.upton@linux.dev>, James Morse <james.morse@arm.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Zenghui Yu <yuzenghui@huawei.com>, Mark Rutland <mark.rutland@arm.com>, Mark Brown <broonie@kernel.org>, Luis Machado <luis.machado@arm.com>, Vladimir Murzin <vladimir.murzin@arm.com>, linux-kernel@vger.kernel.org Subject: Re: [PATCH 04/10] arm64: mops: document boot requirements for MOPS Date: Fri, 24 Mar 2023 01:00:43 +0000 [thread overview] Message-ID: <61b0e30a-568c-d7f6-7b67-e9fc8b68de25@arm.com> (raw) In-Reply-To: <ZBSCObGmIXjyeMA6@arm.com> On 17/03/2023 15:07, Catalin Marinas wrote: > On Thu, Feb 16, 2023 at 04:00:06PM +0000, Kristina Martsenko wrote: >> + For CPUs with Memory Copy and Memory Set instructions (FEAT_MOPS): >> + >> + - If the kernel is entered at EL1 and EL2 is present: >> + >> + - HCRX_EL2.MSCEn (bit 11) must be initialised to 0b1. >> + >> + - HCRX_EL2.MCE2 (bit 10) must be initialised to 0b0. > > Regarding MCE2, does EL1 actually care if EL2 wants to handle all the > memcpy/memset exceptions? No, EL1 does not need to handle the exceptions itself, but I don't see any current use case for allowing EL2 to handle it. If it was allowed, I think booting.txt would need to specify exactly what Linux expects EL2 to do if MCE2 is set (eg, that EL2 handles the exception by reformatting registers, modifying single step state, etc). > There may even be a valid case to do this at > EL2 if you run a guest that uses these instructions but has no clue on > how to deal with the specific exception like WrongOption. Not sure I follow - this series adds the exception handling, so how can a Linux guest not know how to handle the exception? Or do you mean that there may be times when EL1 can't take the exception but EL2 may move it to another CPU, and so EL2 would need to handle the exception? I'm not sure if Linux ever uses mops instructions at times like that. Note that this series does not add support for mops in guests yet. I think booting.txt can be updated when that support is added. Thanks, Kristina _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2023-03-24 1:00 UTC|newest] Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-02-16 16:00 [PATCH 00/10] arm64: support Armv8.8 memcpy instructions in userspace Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-02-16 16:00 ` [PATCH 01/10] KVM: arm64: initialize HCRX_EL2 Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-03-17 14:25 ` Catalin Marinas 2023-03-17 14:25 ` Catalin Marinas 2023-02-16 16:00 ` [PATCH 02/10] arm64: cpufeature: detect FEAT_HCX Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-03-17 14:25 ` Catalin Marinas 2023-03-17 14:25 ` Catalin Marinas 2023-02-16 16:00 ` [PATCH 03/10] KVM: arm64: switch HCRX_EL2 between host and guest Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-02-16 16:20 ` Mark Brown 2023-02-16 16:20 ` Mark Brown 2023-02-22 18:36 ` Kristina Martsenko 2023-02-22 18:36 ` Kristina Martsenko 2023-02-16 16:35 ` Marc Zyngier 2023-02-16 16:35 ` Marc Zyngier 2023-02-22 18:42 ` Kristina Martsenko 2023-02-22 18:42 ` Kristina Martsenko 2023-02-16 16:00 ` [PATCH 04/10] arm64: mops: document boot requirements for MOPS Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-03-17 15:07 ` Catalin Marinas 2023-03-17 15:07 ` Catalin Marinas 2023-03-24 1:00 ` Kristina Martsenko [this message] 2023-03-24 1:00 ` Kristina Martsenko 2023-04-04 10:50 ` Catalin Marinas 2023-04-04 10:50 ` Catalin Marinas 2023-04-11 16:57 ` Kristina Martsenko 2023-04-11 16:57 ` Kristina Martsenko 2023-02-16 16:00 ` [PATCH 05/10] arm64: mops: don't disable host MOPS instructions from EL2 Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-03-17 15:07 ` Catalin Marinas 2023-03-17 15:07 ` Catalin Marinas 2023-02-16 16:00 ` [PATCH 06/10] KVM: arm64: hide MOPS from guests Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-03-17 15:09 ` Catalin Marinas 2023-03-17 15:09 ` Catalin Marinas 2023-02-16 16:00 ` [PATCH 07/10] arm64: mops: handle MOPS exceptions Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-03-17 15:45 ` Catalin Marinas 2023-03-17 15:45 ` Catalin Marinas 2023-02-16 16:00 ` [PATCH 08/10] arm64: mops: handle single stepping after MOPS exception Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-03-17 16:02 ` Catalin Marinas 2023-03-17 16:02 ` Catalin Marinas 2023-02-16 16:00 ` [PATCH 09/10] arm64: mops: detect and enable FEAT_MOPS Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-02-16 16:22 ` Mark Brown 2023-02-16 16:22 ` Mark Brown 2023-03-17 16:03 ` Catalin Marinas 2023-03-17 16:03 ` Catalin Marinas 2023-02-16 16:00 ` [PATCH 10/10] arm64: mops: allow disabling MOPS from the kernel command line Kristina Martsenko 2023-02-16 16:00 ` Kristina Martsenko 2023-03-17 16:04 ` Catalin Marinas 2023-03-17 16:04 ` Catalin Marinas
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