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Message-ID: <28a237e2-5902-4445-a05a-4d1877863ece@arm.com>
Date: Mon, 15 Sep 2025 11:55:26 +0100
From: Steven Price <steven.price@....com>
To: Gavin Shan <gshan@...hat.com>, kvm@...r.kernel.org, kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
Oliver Upton <oliver.upton@...ux.dev>,
Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
<yuzenghui@...wei.com>, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, Joey Gouly <joey.gouly@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
Christoffer Dall <christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>,
linux-coco@...ts.linux.dev,
Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun
<alpergun@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
Emi Kisanuki <fj0570is@...itsu.com>, Vishal Annapurve <vannapurve@...gle.com>
Subject: Re: [PATCH v10 05/43] arm64: RME: Check for RME support at KVM init
On 03/09/2025 12:15, Gavin Shan wrote:
> On 8/21/25 12:55 AM, Steven Price wrote:
>> Query the RMI version number and check if it is a compatible version. A
>> static key is also provided to signal that a supported RMM is available.
>>
>> Functions are provided to query if a VM or VCPU is a realm (or rec)
>> which currently will always return false.
>>
>> Later patches make use of struct realm and the states as the ioctls
>> interfaces are added to support realm and REC creation and destruction.
>>
>> Reviewed-by: Gavin Shan <gshan@...hat.com>
>> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
>> Signed-off-by: Steven Price <steven.price@....com>
>> ---
>> Changes since v8:
>> * No need to guard kvm_init_rme() behind 'in_hyp_mode'.
>> Changes since v6:
>> * Improved message for an unsupported RMI ABI version.
>> Changes since v5:
>> * Reword "unsupported" message from "host supports" to "we want" to
>> clarify that 'we' are the 'host'.
>> Changes since v2:
>> * Drop return value from kvm_init_rme(), it was always 0.
>> * Rely on the RMM return value to identify whether the RSI ABI is
>> compatible.
>> ---
>> arch/arm64/include/asm/kvm_emulate.h | 18 +++++++++
>> arch/arm64/include/asm/kvm_host.h | 4 ++
>> arch/arm64/include/asm/kvm_rme.h | 56 ++++++++++++++++++++++++++++
>> arch/arm64/include/asm/virt.h | 1 +
>> arch/arm64/kvm/Makefile | 2 +-
>> arch/arm64/kvm/arm.c | 5 +++
>> arch/arm64/kvm/rme.c | 56 ++++++++++++++++++++++++++++
>> 7 files changed, 141 insertions(+), 1 deletion(-)
>> create mode 100644 arch/arm64/include/asm/kvm_rme.h
>> create mode 100644 arch/arm64/kvm/rme.c
>>
>
> [...]
>
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index 888f7c7abf54..76177c56f1ef 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -40,6 +40,7 @@
>> #include <asm/kvm_nested.h>
>> #include <asm/kvm_pkvm.h>
>> #include <asm/kvm_ptrauth.h>
>> +#include <asm/kvm_rme.h>
>> #include <asm/sections.h>
>>
>
> Nit: The header file <asm/kvm_rme.h> has been included to <asm/
> kvm_host.h> and
> <linux/kvm_host.h>, which has been included to arm.c. So this explicit
> inclusion
> can be dropped.
While it's true that it could be dropped because of the indirect
include, generally it's better to explicitly include a header file when
you are using the definitions from it. That way the code can be
refactored (e.g. if asm/kvm_host.h is changed to no longer needs the
header it can then safely drop the header include).
We have a similar situation with asm/kvm_asm.h being included both here
and in asm/kvm_host.h (and probably many others, this was just the first
I spotted).
>> #include <kvm/arm_hypercalls.h>
>> @@ -59,6 +60,8 @@ enum kvm_wfx_trap_policy {
>> static enum kvm_wfx_trap_policy kvm_wfi_trap_policy __read_mostly =
>> KVM_WFX_NOTRAP_SINGLE_TASK;
>> static enum kvm_wfx_trap_policy kvm_wfe_trap_policy __read_mostly =
>> KVM_WFX_NOTRAP_SINGLE_TASK;
>> +DEFINE_STATIC_KEY_FALSE(kvm_rme_is_available);
>> +
>> DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
>> DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_base);
>> @@ -2836,6 +2839,8 @@ static __init int kvm_arm_init(void)
>> in_hyp_mode = is_kernel_in_hyp_mode();
>> + kvm_init_rme();
>> +
>> if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
>> cpus_have_final_cap(ARM64_WORKAROUND_1508412))
>> kvm_info("Guests without required CPU erratum workarounds
>> can deadlock system!\n" \
>> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
>> new file mode 100644
>> index 000000000000..67cf2d94cb2d
>> --- /dev/null
>> +++ b/arch/arm64/kvm/rme.c
>> @@ -0,0 +1,56 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (C) 2023 ARM Ltd.
>> + */
>> +
>> +#include <linux/kvm_host.h>
>> +
>> +#include <asm/rmi_cmds.h>
>> +#include <asm/virt.h>
>> +
>> +static int rmi_check_version(void)
>> +{
>> + struct arm_smccc_res res;
>> + unsigned short version_major, version_minor;
>> + unsigned long host_version = RMI_ABI_VERSION(RMI_ABI_MAJOR_VERSION,
>> + RMI_ABI_MINOR_VERSION);
>> +
>> + arm_smccc_1_1_invoke(SMC_RMI_VERSION, host_version, &res);
>> +
>> + if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
>> + return -ENXIO;
>> +
>> + version_major = RMI_ABI_VERSION_GET_MAJOR(res.a1);
>> + version_minor = RMI_ABI_VERSION_GET_MINOR(res.a1);
>> +
>> + if (res.a0 != RMI_SUCCESS) {
>> + unsigned short high_version_major, high_version_minor;
>> +
>> + high_version_major = RMI_ABI_VERSION_GET_MAJOR(res.a2);
>> + high_version_minor = RMI_ABI_VERSION_GET_MINOR(res.a2);
>> +
>> + kvm_err("Unsupported RMI ABI (v%d.%d - v%d.%d) we want v%d.
>> %d\n",
>> + version_major, version_minor,
>> + high_version_major, high_version_minor,
>> + RMI_ABI_MAJOR_VERSION,
>> + RMI_ABI_MINOR_VERSION);
>> + return -ENXIO;
>> + }
>> +
>> + kvm_info("RMI ABI version %d.%d\n", version_major, version_minor);
>> +
>> + return 0;
>> +}
>> +
>> +void kvm_init_rme(void)
>> +{
>> + if (PAGE_SIZE != SZ_4K)
>> + /* Only 4k page size on the host is supported */
>> + return;
>
> Nit: The comment can be moved before the check, something like below.
> Otherwise,
> {} is needed here.
>
> /* Only 4kB page size is supported */
> if (PAGE_SIZE != SZ_4K)
> return;
>
>> +
>> + if (rmi_check_version())
>> + /* Continue without realm support */
>> + return;
>
> Nit: same as above.
Fair enough, I'm never sure what's best here - the comments are for the
error path "Continue without realm support [if we can't agree on a
version]", but it's a single statement so braces aren't needed. Still
the first instance can easily be hoisted above without losing its
meaning, and the second can be extended to clarify.
Thanks,
Steve
>> +
>> + /* Future patch will enable static branch kvm_rme_is_available */
>> +}
>
> Thanks,
> Gavin
>
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