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Date: Fri, 03 Sep 2021 15:43:52 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Juergen Gross <jgross@...e.com>, kvm@...r.kernel.org,
x86@...nel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: maz@...nel.org, ehabkost@...hat.com,
Juergen Gross <jgross@...e.com>,
Jonathan Corbet <corbet@....net>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 2/6] x86/kvm: add boot parameter for adding vcpu-id bits
Juergen Gross <jgross@...e.com> writes:
> 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@...e.com>
> ---
> V2:
> - switch to specifying additional bits (based on comment by Vitaly
> Kuznetsov)
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
> .../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. */
This assumes topology_max_die_per_package() can not be greater than 2,
or 1 additional bit may not suffice, right?
> + }
> +
> + if (!n_bits)
> + n_bits = 1;
Nitpick: AFAIU n_bits can't be zero here as KVM_MAX_VCPUS is still
static. The last patch of the series, however, makes it possible when
max_vcpus = 1 and vcpu_id_add_bits = 0. With this, I'd suggest to move
the check to the last patch.
> +
> + 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
--
Vitaly
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