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Subject[PATCH 3/6] x86/kvm: add boot parameter for maximum vcpu-id
Date
Today the maximum vcpu-id of a kvm guest's vcpu on x86 systems is set
via a #define in a header file.

In order to support higher vcpu-ids without generally increasing the
memory consumption of guests on the host (some guest structures contain
arrays sized by KVM_MAX_VCPU_ID) add a boot parameter for selecting the
maximum vcpu-id. Per default it will still be the current value of
1023, but it can be set manually to higher or lower values.

This requires to allocate the arrays using KVM_MAX_VCPU_ID as the size
dynamically.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++
arch/x86/include/asm/kvm_host.h | 5 ++++-
arch/x86/kvm/ioapic.c | 12 +++++++++++-
arch/x86/kvm/ioapic.h | 4 ++--
arch/x86/kvm/x86.c | 3 +++
5 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbdedc46..99bfa53a2bbd 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2365,6 +2365,14 @@
feature (tagged TLBs) on capable Intel chips.
Default is 1 (enabled)

+ kvm.max_vcpu_id=
+ [KVM,X86] Set the maximum allowed vcpu-id of a guest.
+ Some memory structure sizes depend on this value, so it
+ shouldn't be set too high. Note that each vcpu of a
+ guests needs to have a unique vcpu-id, so a single
+ guest can't have more vcpus than the set value + 1.
+ Default: 1023
+
l1tf= [X86] Control mitigation of the L1TF vulnerability on
affected CPUs

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 9c7ced0e3171..88b1ff898fb9 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -39,7 +39,8 @@

#define KVM_MAX_VCPUS 288
#define KVM_SOFT_MAX_VCPUS 240
-#define KVM_MAX_VCPU_ID 1023
+#define KVM_DEFAULT_MAX_VCPU_ID 1023
+#define KVM_MAX_VCPU_ID max_vcpu_id
/* memory slots that are not exposed to userspace */
#define KVM_PRIVATE_MEM_SLOTS 3

@@ -1511,6 +1512,8 @@ 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 vcpu-id */
+extern unsigned int max_vcpu_id;

extern u64 kvm_mce_cap_supported;

diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
index ff005fe738a4..52e8ea90c914 100644
--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -685,11 +685,21 @@ static const struct kvm_io_device_ops ioapic_mmio_ops = {
int kvm_ioapic_init(struct kvm *kvm)
{
struct kvm_ioapic *ioapic;
+ size_t sz;
int ret;

- ioapic = kzalloc(sizeof(struct kvm_ioapic), GFP_KERNEL_ACCOUNT);
+ sz = sizeof(struct kvm_ioapic) +
+ sizeof(*ioapic->rtc_status.dest_map.map) *
+ BITS_TO_LONGS(KVM_MAX_VCPU_ID + 1) +
+ sizeof(*ioapic->rtc_status.dest_map.vectors) *
+ (KVM_MAX_VCPU_ID + 1);
+ ioapic = kzalloc(sz, GFP_KERNEL_ACCOUNT);
if (!ioapic)
return -ENOMEM;
+ ioapic->rtc_status.dest_map.map = (void *)(ioapic + 1);
+ ioapic->rtc_status.dest_map.vectors =
+ (void *)(ioapic->rtc_status.dest_map.map +
+ BITS_TO_LONGS(KVM_MAX_VCPU_ID + 1));
spin_lock_init(&ioapic->lock);
INIT_DELAYED_WORK(&ioapic->eoi_inject, kvm_ioapic_eoi_inject_work);
kvm->arch.vioapic = ioapic;
diff --git a/arch/x86/kvm/ioapic.h b/arch/x86/kvm/ioapic.h
index bbd4a5d18b5d..623a3c5afad7 100644
--- a/arch/x86/kvm/ioapic.h
+++ b/arch/x86/kvm/ioapic.h
@@ -39,13 +39,13 @@ struct kvm_vcpu;

struct dest_map {
/* vcpu bitmap where IRQ has been sent */
- DECLARE_BITMAP(map, KVM_MAX_VCPU_ID + 1);
+ unsigned long *map;

/*
* Vector sent to a given vcpu, only valid when
* the vcpu's bit in map is set
*/
- u8 vectors[KVM_MAX_VCPU_ID + 1];
+ u8 *vectors;
};


diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e0f4a46649d7..0390d90fd360 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -177,6 +177,9 @@ module_param(force_emulation_prefix, bool, S_IRUGO);
int __read_mostly pi_inject_timer = -1;
module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR);

+unsigned int __read_mostly max_vcpu_id = KVM_DEFAULT_MAX_VCPU_ID;
+module_param(max_vcpu_id, uint, S_IRUGO);
+
/*
* Restoring the host value for MSRs that are only consumed when running in
* usermode, e.g. SYSCALL MSRs and TSC_AUX, can be deferred until the CPU
--
2.26.2
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