From: Juergen Gross <jgross@suse.com>
To: kvm@vger.kernel.org, x86@kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org
Cc: maz@kernel.org, ehabkost@redhat.com,
Juergen Gross <jgross@suse.com>, Jonathan Corbet <corbet@lwn.net>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: [PATCH v2 6/6] x86/kvm: add boot parameter for setting max number of vcpus per guest
Date: Fri, 3 Sep 2021 15:08:07 +0200 [thread overview]
Message-ID: <20210903130808.30142-7-jgross@suse.com> (raw)
In-Reply-To: <20210903130808.30142-1-jgross@suse.com>
Today the maximum number of vcpus of a kvm guest is set via a #define
in a header file.
In order to support higher vcpu numbers for guests without generally
increasing the memory consumption of guests on the host especially on
very large systems add a boot parameter for specifying the number of
allowed vcpus for guests.
The default will still be the current setting of 288. The value 0 has
the special meaning to limit the number of possible vcpus to the
number of possible cpus of the host.
Signed-off-by: Juergen Gross <jgross@suse.com>
---
Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
arch/x86/include/asm/kvm_host.h | 5 ++++-
arch/x86/kvm/x86.c | 9 ++++++++-
3 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 37e194299311..b9641c9989ef 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2435,6 +2435,13 @@
feature (tagged TLBs) on capable Intel chips.
Default is 1 (enabled)
+ kvm.max_vcpus= [KVM,X86] Set the maximum allowed numbers of vcpus per
+ guest. The special value 0 sets the limit to the number
+ of physical cpus possible on the host (including not
+ yet hotplugged cpus). Higher values will result in
+ slightly higher memory consumption per guest.
+ Default: 288
+
kvm.vcpu_id_add_bits=
[KVM,X86] The vcpu-ids of guests are sparse, as they
are constructed by bit-wise concatenation of the ids of
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6c28d0800208..a4ab387b0e1c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -38,7 +38,8 @@
#define __KVM_HAVE_ARCH_VCPU_DEBUGFS
-#define KVM_MAX_VCPUS 288
+#define KVM_DEFAULT_MAX_VCPUS 288
+#define KVM_MAX_VCPUS max_vcpus
#define KVM_SOFT_MAX_VCPUS 240
#define KVM_MAX_VCPU_ID kvm_max_vcpu_id()
/* memory slots that are not exposed to userspace */
@@ -1588,6 +1589,8 @@ extern u64 kvm_max_tsc_scaling_ratio;
extern u64 kvm_default_tsc_scaling_ratio;
/* bus lock detection supported? */
extern bool kvm_has_bus_lock_exit;
+/* maximum number of vcpus per guest */
+extern unsigned int max_vcpus;
/* maximum vcpu-id */
unsigned int kvm_max_vcpu_id(void);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ff142b6dd00c..49c3d91c559e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -188,9 +188,13 @@ module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR);
static int __read_mostly vcpu_id_add_bits = -1;
module_param(vcpu_id_add_bits, int, S_IRUGO);
+unsigned int __read_mostly max_vcpus = KVM_DEFAULT_MAX_VCPUS;
+module_param(max_vcpus, uint, S_IRUGO);
+EXPORT_SYMBOL_GPL(max_vcpus);
+
unsigned int kvm_max_vcpu_id(void)
{
- int n_bits = fls(KVM_MAX_VCPUS - 1);
+ int n_bits = fls(max_vcpus - 1);
if (vcpu_id_add_bits < -1 || vcpu_id_add_bits > (32 - n_bits)) {
pr_err("Invalid value of vcpu_id_add_bits=%d parameter!\n",
@@ -11033,6 +11037,9 @@ int kvm_arch_hardware_setup(void *opaque)
if (boot_cpu_has(X86_FEATURE_XSAVES))
rdmsrl(MSR_IA32_XSS, host_xss);
+ if (max_vcpus == 0)
+ max_vcpus = num_possible_cpus();
+
kvm_pcpu_vcpu_mask = __alloc_percpu(KVM_VCPU_MASK_SZ,
sizeof(unsigned long));
kvm_hv_vp_bitmap = __alloc_percpu(KVM_HV_VPMAP_SZ, sizeof(u64));
--
2.26.2
next prev parent reply other threads:[~2021-09-03 13:08 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-03 13:08 [PATCH v2 0/6] x86/kvm: add boot parameters for max vcpu configs Juergen Gross
2021-09-03 13:08 ` [PATCH v2 1/6] x86/kvm: remove non-x86 stuff from arch/x86/kvm/ioapic.h Juergen Gross
2021-09-03 13:08 ` [PATCH v2 2/6] x86/kvm: add boot parameter for adding vcpu-id bits Juergen Gross
2021-09-03 13:43 ` Vitaly Kuznetsov
2021-09-03 13:53 ` Juergen Gross
2021-09-03 19:48 ` Eduardo Habkost
2021-09-06 4:46 ` Juergen Gross
2021-09-28 16:41 ` Paolo Bonzini
2021-09-03 13:08 ` [PATCH v2 3/6] x86/kvm: introduce per cpu vcpu masks Juergen Gross
2021-09-03 16:05 ` Eduardo Habkost
2021-09-06 4:34 ` Juergen Gross
2021-09-07 18:34 ` Eduardo Habkost
2021-09-08 8:41 ` Vitaly Kuznetsov
2021-09-03 13:08 ` [PATCH v2 4/6] kvm: use kvfree() in kvm_arch_free_vm() Juergen Gross
2021-09-28 16:48 ` Paolo Bonzini
2021-09-03 13:08 ` [PATCH v2 5/6] kvm: allocate vcpu pointer array separately Juergen Gross
2021-09-03 14:41 ` Marc Zyngier
2021-09-06 4:33 ` Juergen Gross
2021-09-06 9:46 ` Marc Zyngier
2021-09-09 20:28 ` Sean Christopherson
2021-09-03 13:08 ` Juergen Gross [this message]
2021-09-06 0:45 ` [PATCH v2 6/6] x86/kvm: add boot parameter for setting max number of vcpus per guest Yao Yuan
2021-09-06 4:47 ` Juergen Gross
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210903130808.30142-7-jgross@suse.com \
--to=jgross@suse.com \
--cc=bp@alien8.de \
--cc=corbet@lwn.net \
--cc=ehabkost@redhat.com \
--cc=hpa@zytor.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maz@kernel.org \
--cc=mingo@redhat.com \
--cc=pbonzini@redhat.com \
--cc=seanjc@google.com \
--cc=tglx@linutronix.de \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).