[PATCH v2 2/6] x86/kvm: add boot parameter for adding vcpu-id bits

[Juergen Gross]

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 adding some
bits to the vcpu-id. Additional bits are needed as the vcpu-id is
constructed via bit-wise concatenation of socket-id, core-id, etc.
As those ids maximum values are not always a power of 2, the vcpu-ids
are sparse.

The additional number of bits needed is basically the number of
topology levels with a non-power-of-2 maximum value, excluding the top
most level.

The default value of the new parameter will be to take the correct
setting from the host's topology.

Calculating the maximum vcpu-id dynamically requires to allocate the
arrays using KVM_MAX_VCPU_ID as the size dynamically.

Signed-of-by: Juergen Gross <jgross@xxxxxxxx>
---
V2:
- switch to specifying additional bits (based on comment by Vitaly
  Kuznetsov)

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 .../admin-guide/kernel-parameters.txt         | 18 ++++++++++++
 arch/x86/include/asm/kvm_host.h               |  4 ++-
 arch/x86/kvm/ioapic.c                         | 12 +++++++-
 arch/x86/kvm/ioapic.h                         |  4 +--
 arch/x86/kvm/x86.c                            | 29 +++++++++++++++++++
 5 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 84dc5790741b..37e194299311 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2435,6 +2435,24 @@
 			feature (tagged TLBs) on capable Intel chips.
 			Default is 1 (enabled)
 
+	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
+			the different topology levels (sockets, cores, threads).
+
+			This parameter specifies how many additional bits the
+			maximum vcpu-id needs compared to the maximum number of
+			vcpus.
+
+			Normally this value is the number of topology levels
+			without the threads level and without the highest
+			level.
+
+			The special value -1 can be used to support guests
+			with the same topology is the host.
+
+			Default: -1
+
 	l1d_flush=	[X86,INTEL]
 			Control mitigation for L1D based snooping vulnerability.
 
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index af6ce8d4c86a..3513edee8e22 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -39,7 +39,7 @@
 
 #define KVM_MAX_VCPUS 288
 #define KVM_SOFT_MAX_VCPUS 240
-#define KVM_MAX_VCPU_ID 1023
+#define KVM_MAX_VCPU_ID kvm_max_vcpu_id()
 /* memory slots that are not exposed to userspace */
 #define KVM_PRIVATE_MEM_SLOTS 3
 
@@ -1588,6 +1588,8 @@ 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 */
+unsigned int kvm_max_vcpu_id(void);
 
 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 e5d5c5ed7dd4..6b6f38f0b617 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -78,6 +78,7 @@
 #include <asm/intel_pt.h>
 #include <asm/emulate_prefix.h>
 #include <asm/sgx.h>
+#include <asm/topology.h>
 #include <clocksource/hyperv_timer.h>
 
 #define CREATE_TRACE_POINTS
@@ -184,6 +185,34 @@ 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);
 
+static int __read_mostly vcpu_id_add_bits = -1;
+module_param(vcpu_id_add_bits, int, S_IRUGO);
+
+unsigned int kvm_max_vcpu_id(void)
+{
+	int n_bits = fls(KVM_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",
+		       vcpu_id_add_bits);
+		vcpu_id_add_bits = -1;
+	}
+
+	if (vcpu_id_add_bits >= 0) {
+		n_bits += vcpu_id_add_bits;
+	} else {
+		n_bits++;		/* One additional bit for core level. */
+		if (topology_max_die_per_package() > 1)
+			n_bits++;	/* One additional bit for die level. */
+	}
+
+	if (!n_bits)
+		n_bits = 1;
+
+	return (1U << n_bits) - 1;
+}
+EXPORT_SYMBOL_GPL(kvm_max_vcpu_id);
+
 /*
  * 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