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Date: Mon, 22 Jan 2024 18:07:32 +0000
From: James Morse <james.morse@....com>
To: Amit Singh Tomar <amitsinght@...vell.com>, "x86@...nel.org"
<x86@...nel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>
Cc: Fenghua Yu <fenghua.yu@...el.com>,
Reinette Chatre <reinette.chatre@...el.com>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>,
Babu Moger <Babu.Moger@....com>,
"shameerali.kolothum.thodi@...wei.com"
<shameerali.kolothum.thodi@...wei.com>,
D Scott Phillips OS <scott@...amperecomputing.com>,
"carl@...amperecomputing.com" <carl@...amperecomputing.com>,
Linu Cherian <lcherian@...vell.com>,
"bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>,
"tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>,
"baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
Jamie Iles <quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
"peternewman@...gle.com" <peternewman@...gle.com>,
"dfustini@...libre.com" <dfustini@...libre.com>,
"muhammad.zahid@...ia.com" <muhammad.zahid@...ia.com>
Subject: Re: [EXT] [PATCH v7 06/24] x86/resctrl: Access per-rmid structures by
index
Hi Amit,
On 21/01/2024 10:27, Amit Singh Tomar wrote:
> -----Original Message-----
> From: James Morse <james.morse@....com>
> Sent: Monday, December 11, 2023 8:03 PM
> To: Amit Singh Tomar <amitsinght@...vell.com>; x86@...nel.org; linux-kernel@...r.kernel.org
> Cc: Fenghua Yu <fenghua.yu@...el.com>; Reinette Chatre <reinette.chatre@...el.com>; Thomas Gleixner <tglx@...utronix.de>; Ingo Molnar <mingo@...hat.com>; Borislav Petkov <bp@...en8.de>; H Peter Anvin <hpa@...or.com>; Babu Moger <Babu.Moger@....com>; shameerali.kolothum.thodi@...wei.com; D Scott Phillips OS <scott@...amperecomputing.com>; carl@...amperecomputing.com; Linu Cherian <lcherian@...vell.com>; bobo.shaobowang@...wei.com; tan.shaopeng@...itsu.com; baolin.wang@...ux.alibaba.com; Jamie Iles <quic_jiles@...cinc.com>; Xin Hao <xhao@...ux.alibaba.com>; peternewman@...gle.com; dfustini@...libre.com; muhammad.zahid@...ia.com
> Subject: Re: [EXT] [PATCH v7 06/24] x86/resctrl: Access per-rmid structures by index
> On 31/10/2023 07:43, Amit Singh Tomar wrote:
>> -----Original Message-----
>> From: James Morse <james.morse@....com>
>> Sent: Wednesday, October 25, 2023 11:33 PM
>> Subject: [EXT] [PATCH v7 06/24] x86/resctrl: Access per-rmid
>> structures by index
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
>> b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 2a0233cd0bc9..c02cf32cd17c 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -735,19 +768,20 @@ void mbm_setup_overflow_handler(struct
>> rdt_domain *dom, unsigned long delay_ms)
>>
>> static int dom_data_init(struct rdt_resource *r) {
>> + u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>> struct rmid_entry *entry = NULL;
>> - int i, nr_rmids;
>> + u32 idx;
>> + int i;
>>
>> - nr_rmids = r->num_rmid;
>> - rmid_ptrs = kcalloc(nr_rmids, sizeof(struct rmid_entry), GFP_KERNEL);
>> + rmid_ptrs = kcalloc(idx_limit, sizeof(struct rmid_entry),
>> +GFP_KERNEL);
>>
>> [>>] Is there a chance, it could result in "ZERO_SIZE_PTR", and we should guard it against ZERO_OR_NULL_PTR in the following if condition?
>> It might be related, while testing the snapshot[1] (and subsequent snapshots has similar change) on x86 platform, Zahid is seeing Kernel panic:
>>
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__git.kernel.org_pu
>> b_scm_linux_kernel_git_morse_linux.git_tree_fs_resctrl_monitor.c-3Fh-3
>> Dmpam_snapshot_v6.2-23n695&d=DwICaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=V_GK7jR
>> uCHDErm6txmgDK1-MbUihtnSQ3gPgB-A-JKU&m=yHcjuc1ZrYfPWXGxTPifeglinf_gMfy
>> AgnvZfOw-ZD2zRG8G61IfH8hignwaxlV6&s=X3Ie_NqTHtzN2ttkl3yiTYHzNpkWW2wPPI
>> DJ7XTWW40&e=
>
> Interesting - I didn't think this could happen. Could you share the full splat?
(this bit here is your reply?:)
> Unfortunately, I don't have access to the test set-up where this splat has been observed.
> However, I have requested Zahid (Cc) to provide the splat logs.
> Additionally, from what I've learned, this splat has been observed on an x86 machine that
> doesn't support monitor groups. Do you see this as problem?
> This would imply idx_limit was zero, so boot_cpu_data.x86_cache_max_rmid would be -1.
> But wouldn't this happen before this patch? idx_limit has the same value as nr_rmids on x86,
> its only MPAM that needs a different value.
Your 'doesn't support monitor groups' explains why boot_cpu_data.x86_cache_max_rmid is -1.
As you've said you're testing the whole tree - not this series, I suspect this is coming
from "x86/resctrl: Move monitor init work to a resctrl init call", which moves
initialisation of filesystem structures to filesystem code.
It looks like I missed that get_rdt_mon_resources() can bale out before calling
rdt_get_mon_l3_config(), which I think would explain what you hint at here.
Adding this to the "x86/resctrl: Move monitor init work to a resctrl init call" should fix
that. (It'll be in the next snapshot I push)
---------------------%<---------------------
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index b3f245c85e00..791554db7c69 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -1030,12 +1030,14 @@ int resctrl_mon_resource_init(void)
struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
int ret;
+ if (!r->mon_capable)
+ return 0;
+
ret = dom_data_init(r);
if (ret)
return ret;
- if (r->mon_capable)
- l3_mon_evt_init(r);
+ l3_mon_evt_init(r);
return 0;
}
---------------------%<---------------------
Thanks,
James
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