From: "Michal Koutný" <mkoutny@suse.com>
To: Vipin Sharma <vipinsh@google.com>
Cc: tj@kernel.org, rdunlap@infradead.org, thomas.lendacky@amd.com,
brijesh.singh@amd.com, jon.grimm@amd.com,
eric.vantassell@amd.com, pbonzini@redhat.com, hannes@cmpxchg.org,
frankja@linux.ibm.com, borntraeger@de.ibm.com, corbet@lwn.net,
seanjc@google.com, vkuznets@redhat.com, wanpengli@tencent.com,
jmattson@google.com, joro@8bytes.org, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
gingell@google.com, rientjes@google.com, dionnaglaze@google.com,
kvm@vger.kernel.org, x86@kernel.org, cgroups@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [Patch v3 1/2] cgroup: sev: Add misc cgroup controller
Date: Thu, 11 Mar 2021 19:59:03 +0100 [thread overview]
Message-ID: <YEpod5X29YqMhW/g@blackbook> (raw)
In-Reply-To: <20210304231946.2766648-2-vipinsh@google.com>
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Hi Vipin.
On Thu, Mar 04, 2021 at 03:19:45PM -0800, Vipin Sharma <vipinsh@google.com> wrote:
> arch/x86/kvm/svm/sev.c | 65 +++++-
> arch/x86/kvm/svm/svm.h | 1 +
> include/linux/cgroup_subsys.h | 4 +
> include/linux/misc_cgroup.h | 130 +++++++++++
> init/Kconfig | 14 ++
> kernel/cgroup/Makefile | 1 +
> kernel/cgroup/misc.c | 402 ++++++++++++++++++++++++++++++++++
Given different two-fold nature (SEV caller vs misc controller) of some
remarks below, I think it makes sense to split this into two patches:
a) generic controller implementation,
b) hooking the controller into SEV ASIDs management.
> +#ifndef CONFIG_KVM_AMD_SEV
> +/*
> + * When this config is not defined, SEV feature is not supported and APIs in
> + * this file are not used but this file still gets compiled into the KVM AMD
> + * module.
> + *
> + * We will not have MISC_CG_RES_SEV and MISC_CG_RES_SEV_ES entries in the enum
> + * misc_res_type {} defined in linux/misc_cgroup.h.
BTW, was there any progress on conditioning sev.c build on
CONFIG_KVM_AMD_SEV? (So that the defines workaround isn't needeed.)
> static int sev_asid_new(struct kvm_sev_info *sev)
> {
> - int pos, min_asid, max_asid;
> + int pos, min_asid, max_asid, ret;
> bool retry = true;
> + enum misc_res_type type;
> +
> + type = sev->es_active ? MISC_CG_RES_SEV_ES : MISC_CG_RES_SEV;
> + sev->misc_cg = get_current_misc_cg();
> + ret = misc_cg_try_charge(type, sev->misc_cg, 1);
It may be safer to WARN_ON(sev->misc_cg) at this point (see below).
> [...]
> +e_uncharge:
> + misc_cg_uncharge(type, sev->misc_cg, 1);
> + put_misc_cg(sev->misc_cg);
> + return ret;
vvv
> @@ -140,6 +171,10 @@ static void sev_asid_free(int asid)
> }
>
> mutex_unlock(&sev_bitmap_lock);
> +
> + type = sev->es_active ? MISC_CG_RES_SEV_ES : MISC_CG_RES_SEV;
> + misc_cg_uncharge(type, sev->misc_cg, 1);
> + put_misc_cg(sev->misc_cg);
It may be safer to set sev->misc_cg to NULL here.
(IIUC, with current asid_{new,free} calls it shouldn't matter but why to
rely on it in the future.)
> +++ b/kernel/cgroup/misc.c
> [...]
> +static void misc_cg_reduce_charge(enum misc_res_type type, struct misc_cg *cg,
> + unsigned long amount)
misc_cg_cancel_charge seems to be a name more consistent with what we
already have in pids and memory controller.
> +static ssize_t misc_cg_max_write(struct kernfs_open_file *of, char *buf,
> + size_t nbytes, loff_t off)
> +{
> [...]
> +
> + if (!strcmp(MAX_STR, buf)) {
> + max = ULONG_MAX;
MAX_NUM for consistency with other places.
> + } else {
> + ret = kstrtoul(buf, 0, &max);
> + if (ret)
> + return ret;
> + }
> +
> + cg = css_misc(of_css(of));
> +
> + if (misc_res_capacity[type])
> + cg->res[type].max = max;
In theory, parallel writers can clash here, so having the limit atomic
type to prevent this would resolve it. See also commit a713af394cf3
("cgroup: pids: use atomic64_t for pids->limit").
> +static int misc_cg_current_show(struct seq_file *sf, void *v)
> +{
> + int i;
> + struct misc_cg *cg = css_misc(seq_css(sf));
> +
> + for (i = 0; i < MISC_CG_RES_TYPES; i++) {
> + if (misc_res_capacity[i])
Since there can be some residual charges after removing capacity (before
draining), maybe the condition along the line
if (misc_res_capacity[i] || atomic_long_read(&cg->res[i].usage))
would be more informative for debugging.
> +static int misc_cg_capacity_show(struct seq_file *sf, void *v)
> +{
> + int i;
> + unsigned long cap;
> +
> + for (i = 0; i < MISC_CG_RES_TYPES; i++) {
> + cap = READ_ONCE(misc_res_capacity[i]);
Why is READ_ONCE only here and not in other places that (actually) check
against the set capacity value? Also, there should be a paired
WRITE_ONCCE in misc_cg_set_capacity().
Thanks,
Michal
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next prev parent reply other threads:[~2021-03-11 18:59 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 23:19 [Patch v3 0/2] cgroup: New misc cgroup controller Vipin Sharma
2021-03-04 23:19 ` [Patch v3 1/2] cgroup: sev: Add " Vipin Sharma
2021-03-11 18:59 ` Michal Koutný [this message]
2021-03-12 19:07 ` Vipin Sharma
2021-03-15 18:34 ` Michal Koutný
2021-03-12 19:48 ` Vipin Sharma
2021-03-12 20:51 ` Sean Christopherson
2021-03-12 21:18 ` Tom Lendacky
2021-03-19 21:28 ` Jacob Pan
2021-03-22 18:54 ` Vipin Sharma
2021-03-24 16:17 ` Jacob Pan
2021-03-24 22:09 ` Vipin Sharma
2021-03-04 23:19 ` [Patch v3 2/2] cgroup: sev: Miscellaneous cgroup documentation Vipin Sharma
2021-03-07 12:48 ` [Patch v3 0/2] cgroup: New misc cgroup controller Tejun Heo
2021-03-11 18:58 ` Michal Koutný
2021-03-11 19:39 ` Tejun Heo
2021-03-12 17:49 ` Vipin Sharma
2021-03-15 19:10 ` Michal Koutný
2021-03-22 18:24 ` Vipin Sharma
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