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[175.34.8.244]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1b5031468b7sm2689566c88.5.2026.11.12.15.42.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Nov 2026 15:42:27 -0800 (PST) Message-ID: Date: Fri, 13 Nov 2026 09:42:21 +1000 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/3] arm_mpam: resctrl: Only enable CDP on a resource that supports it To: Jinjie Ruan , james.morse@arm.com, ben.horgan@arm.com, reinette.chatre@intel.com, fenghuay@nvidia.com, zengheng4@huawei.com, tan.shaopeng@jp.fujitsu.com, jic23@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20261111081316.3828283-1-ruanjinjie@huawei.com> <20261111081316.3828283-3-ruanjinjie@huawei.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20261111081316.3828283-3-ruanjinjie@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/11/26 6:13 PM, Jinjie Ruan wrote: > resctrl_arch_set_cdp_enabled() enables CDP for any cache level that is > requested, even one that has no MPAM cache controls. Mounting resctrl > with -o cdpl2 when only L3 can allocate still turns CDP emulation on for > the whole system, so every CLOSID takes two PARTIDs while resctrl keeps > its CLOSID count at the number of PARTIDs. Control groups in the upper > half then map to PARTIDs beyond mpam_partid_max, which index past the > configuration and monitor arrays and program out of range PARTIDs into > the MSCs. On QEMU with 5 PARTIDs the first monitor read after creating > 2 control groups raises MSMONCFG_ID_RANGE for PARTID 5, and MPAM is > disabled. > > Do not enable CDP when a resource cannot allocate or is not CDP capable, > as x86 does, so the mount fails instead. Only the enable path is checked, > since unmount disables CDP on both cache levels to restore the MBA control. > > A system where only MBA can allocate, or that only has monitors, now > fails a mount with CDP as well: CDP hides the MBA control because > mbw_max is a per-PARTID maximum, leaving nothing for CDP to apply to. > > Fixes: 6789fb99282c ("arm_mpam: resctrl: Add CDP emulation") > Link: https://sashiko.dev/#/bug/linux-05c19551-0bba-4a06-aa2c-3c90fab5853d > Suggested-by: Ben Horgan > Signed-off-by: Jinjie Ruan > Cc: # 7.1+ > --- > drivers/resctrl/mpam_resctrl.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c > index 573617ba09df..afa3c084c475 100644 > --- a/drivers/resctrl/mpam_resctrl.c > +++ b/drivers/resctrl/mpam_resctrl.c > @@ -222,6 +222,10 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level rid, bool enable) > if (enable && mpam_partid_max < 1) > return -EINVAL; > > + if (enable && (!mpam_resctrl_controls[rid].resctrl_res.alloc_capable || > + !mpam_resctrl_controls[rid].resctrl_res.cdp_capable)) > + return -EINVAL; > + x86 only checks 'cdp_capable', so this check isn't exactly same as to what's done on x86, as claimed in the commit log? int resctrl_arch_set_cdp_enabled(enum resctrl_res_level l, bool enable) { struct rdt_hw_resource *hw_res = &rdt_resources_all[l]; if (!hw_res->r_resctrl.cdp_capable) return -EINVAL; : } > /* > * resctrl_arch_set_cdp_enabled() is only called with enable set to > * false on error and unmount. Thanks, Gavin