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[175.34.8.244]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2db1495acf7sm57511075ad.25.2026.09.08.03.59.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Sep 2026 03:59:56 -0700 (PDT) Message-ID: <9706a0b9-b686-4502-bfae-08aabe05fb84@redhat.com> Date: Tue, 8 Sep 2026 20:59:45 +1000 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v17 3/7] firmware: arm_rmm: Configure the RMM with the host's page size To: Kohei Enju Cc: Suzuki K Poulose , kvm@vger.kernel.org, kvmarm@lists.linux.dev, maz@kernel.org, will@kernel.org, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, steven.price@arm.com, aneesh.kumar@kernel.org, oupton@kernel.org, joey.gouly@arm.com, tabba@google.com, yuzenghui@huawei.com, linux-coco@lists.linux.dev, gankulkarni@os.amperecomputing.com, sdonthineni@nvidia.com, alpergun@google.com, fj0570is@fujitsu.com, WeiLin.Chang@arm.com, lpieralisi@kernel.org References: <20260907095942.1140734-1-suzuki.poulose@arm.com> <20260907095942.1140734-4-suzuki.poulose@arm.com> <10893135-4757-44de-91b5-180a9774d868@redhat.com> Content-Language: en-US From: Gavin Shan In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Kohei, On 9/8/26 6:00 PM, Kohei Enju wrote: > Hi Gavin, > > On 09/08 17:04, Gavin Shan wrote: >> Hi Suzuki, >> >> On 9/7/26 7:59 PM, Suzuki K Poulose wrote: >>> From: Steven Price >>> >>> RMM v2.0 brings the ability to set the RMM's granule size. Check the >>> feature registers and configure the RMM so that it matches the host's >>> page size. This means that operations can be done with a granularity >>> equal to PAGE_SIZE. >>> >>> Signed-off-by: Steven Price >>> Signed-off-by: Suzuki K Poulose >>> --- >>> Changes since v15: >>> * Actually check the feature register for the host's page-size support. >>> Changes since v14: >>> * Move the implementation into drivers/firmware/arm_rmm. >>> Changes since v13: >>> * Moved out of KVM. >>> --- >>> drivers/firmware/arm_rmm/rmi.c | 58 ++++++++++++++++++++++++++++++++++ >>> include/linux/arm-rmi-cmds.h | 17 ++++++++++ >>> 2 files changed, 75 insertions(+) >>> >>> diff --git a/drivers/firmware/arm_rmm/rmi.c b/drivers/firmware/arm_rmm/rmi.c >>> index 008a783407b4e..76f91c145e1fd 100644 >>> --- a/drivers/firmware/arm_rmm/rmi.c >>> +++ b/drivers/firmware/arm_rmm/rmi.c >>> @@ -77,6 +77,60 @@ static int rmi_read_features(void) >>> return 0; >>> } >>> +static int rmi_configure(void) >>> +{ >>> + unsigned long granule_feature; >>> + unsigned long granule_size; >>> + int ret = 0; >>> + struct rmm_config *config; >>> + >>> + switch (PAGE_SIZE) { >>> + case SZ_4K: >>> + granule_size = RMI_GRANULE_SIZE_4KB; >>> + granule_feature = RMI_FEATURE_REGISTER_1_RMI_GRAN_SZ_4KB; >>> + break; >>> + case SZ_16K: >>> + granule_size = RMI_GRANULE_SIZE_16KB; >>> + granule_feature = RMI_FEATURE_REGISTER_1_RMI_GRAN_SZ_16KB; >>> + break; >>> + case SZ_64K: >>> + granule_size = RMI_GRANULE_SIZE_64KB; >>> + granule_feature = RMI_FEATURE_REGISTER_1_RMI_GRAN_SZ_64KB; >>> + break; >>> + default: >>> + BUILD_BUG(); >>> + } >>> + >>> + if (!(rmi_feat_reg(1) & granule_feature)) { >>> + pr_err("RMM does not support %luKB granules\n", >>> + PAGE_SIZE >> 10); >>> + return -ENXIO; >>> + } >>> + >>> + config = (struct rmm_config *)get_zeroed_page(GFP_KERNEL); >>> + if (!config) >>> + return -ENOMEM; >> >> An error message is needed here. >> >> if (!config) { >> pr_err("Unable to alloc RMM config memory\n"); >> return -ENOMEM; >> } > > I largely agree with your suggestions, and they look reasonable to me. > > However, wouldn't this be redundant? Since __GFP_NOWARN is not set, the > page allocator would normally emit an allocation failure warning with a > stack trace anyway. > > I don't have a strong preference, but as per "14) Allocating memory" in > the coding style, I believe it would be considered unnecessary. > You're correct that the error message is most likely redundant here and we needn't it. However, it's notable the allocation failure warning and stack trace isn't 100% raised when looking at mm/page_alloc.c::warn_alloc(). At least, it depends on !__ratelimit(&nopage_rs) even it's less likely to happen. Similarly, there are conditions to raise a warning and stack track in case of the injected allocation error in lib/fault-inject.c::fail_dump(). Thanks, Gavin > Thanks, > Kohei > >> >>> + >>> + config->rmi_granule_size = granule_size; >>> + >>> + /* >>> + * For now we set the tracking_region_size to 0 which is the only option >>> + * for 4KB PAGE_SIZE (1GB for 4KB PAGE_SIZE, 32MB/512MB for 16KB/64KB). >>> + * TODO: Support other tracking sizes via Kconfig option for other >>> + * PAGE_SIZES >>> + */ >>> + config->tracking_region_size = 0; >>> + >>> + ret = rmi_rmm_config_set(virt_to_phys(config)); >>> + if (ret) { >>> + pr_err("RMM config set failed\n"); >>> + ret = -EINVAL; >>> + } >> >> The error code from rmi_rmm_config_set() is indicative sometimes. Also, -ENXIO >> would be more appropriate than -EINVAL? >> >> if (ret) { >> pr_err("RMM config set failed (%d)\n", ret); >> ret = -ENXIO; >> } >> >>> + >>> + free_page((unsigned long)config); >>> + return ret; >>> +} >>> + >>> static int __init arm64_init_rmi(void) >>> { >>> int ret; >>> @@ -90,6 +144,10 @@ static int __init arm64_init_rmi(void) >>> if (ret) >>> return ret; >>> + ret = rmi_configure(); >>> + if (ret) >>> + return ret; >>> + >>> return 0; >>> } >>> diff --git a/include/linux/arm-rmi-cmds.h b/include/linux/arm-rmi-cmds.h >>> index 2fb1f7f86d71e..9aa27697e2377 100644 >>> --- a/include/linux/arm-rmi-cmds.h >>> +++ b/include/linux/arm-rmi-cmds.h >>> @@ -12,6 +12,23 @@ >>> unsigned long rmi_feat_reg(unsigned long id); >>> +/** >>> + * rmi_rmm_config_set() - Configure the RMM >>> + * @cfg_ptr: PA of a struct rmm_config >>> + * >>> + * Sets configuration options on the RMM. >>> + * >>> + * Return: RMI return code >>> + */ >>> +static inline int rmi_rmm_config_set(unsigned long cfg_ptr) >>> +{ >>> + struct arm_smccc_res res; >>> + >>> + arm_smccc_1_1_invoke(SMC_RMI_RMM_CONFIG_SET, cfg_ptr, &res); >>> + >>> + return res.a0; >>> +} >>> + >> >> rmi_rmm_config_set() is used for once by rmi.c::rmi_configure(), I would not expose >> rmi_rmm_config_set() by combining the logic to rmi.c::rmi_configure(). >> >>> /** >>> * rmi_features() - Read feature register >>> * @index: Feature register index >> >> Thanks, >> Gavin >> >