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Date: Mon, 23 May 2022 15:27:10 -0700
From: Sagi Shahar <sagis@...gle.com>
To: "Yamahata, Isaku" <isaku.yamahata@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
Erdem Aktas <erdemaktas@...gle.com>,
Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v6 003/104] KVM: Refactor CPU compatibility check on
module initialiization
On Thu, May 5, 2022 at 11:15 AM <isaku.yamahata@...el.com> wrote:
>
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> Although non-x86 arch doesn't break as long as I inspected code, it's by
> code inspection. This should be reviewed by each arch maintainers.
>
> kvm_init() checks CPU compatibility by calling
> kvm_arch_check_processor_compat() on all online CPUs. Move the callback
> to hardware_enable_nolock() and add hardware_enable_all() and
> hardware_disable_all().
> Add arch specific callback kvm_arch_post_hardware_enable_setup() for arch
> to do arch specific initialization that required hardware_enable_all().
There's no reference to kvm_arch_post_hardware_enable_setup in this
patch. Looks like it's introduced in a later patch in the series.
This patch might be clearer if the kvm_arch_post_hardware_enable_setup
is introduced and used here. Otherwise, the commit log should be
updated to make it clear that kvm_arch_post_hardware_enable_setup is
introduced in a later patch in the series.
> This makes a room for TDX module to initialize on kvm module loading. TDX
> module requires all online cpu to enable VMX by VMXON.
>
> If kvm_arch_hardware_enable/disable() depend on (*) part, such dependency
> must be called before kvm_init(). In fact kvm_intel() does. Although
> other arch doesn't as long as I checked as follows, it should be reviewed
> by each arch maintainers.
>
> Before this patch:
> - Arch module initialization
> - kvm_init()
> - kvm_arch_init()
> - kvm_arch_check_processor_compat() on each CPUs
> - post arch specific initialization ---- (*)
>
> - when creating/deleting first/last VM
> - kvm_arch_hardware_enable() on each CPUs --- (A)
> - kvm_arch_hardware_disable() on each CPUs --- (B)
>
> After this patch:
> - Arch module initialization
> - kvm_init()
> - kvm_arch_init()
> - kvm_arch_hardware_enable() on each CPUs (A)
> - kvm_arch_check_processor_compat() on each CPUs
> - kvm_arch_hardware_disable() on each CPUs (B)
> - post arch specific initialization --- (*)
>
> Code inspection result:
> (A)/(B) can depend on (*) before this patch. If there is dependency, such
> initialization must be moved before kvm_init() with this patch. VMX does
> in fact. As long as I inspected other archs and find only mips has it.
>
> - arch/mips/kvm/mips.c
> module init function, kvm_mips_init(), does some initialization after
> kvm_init(). Compile test only. Needs review.
>
> - arch/x86/kvm/x86.c
> - uses vm_list which is statically initialized.
> - static_call(kvm_x86_hardware_enable)();
> - SVM: (*) is empty.
> - VMX: needs fix
>
> - arch/powerpc/kvm/powerpc.c
> kvm_arch_hardware_enable/disable() are nop
>
> - arch/s390/kvm/kvm-s390.c
> kvm_arch_hardware_enable/disable() are nop
>
> - arch/arm64/kvm/arm.c
> module init function, arm_init(), calls only kvm_init().
> (*) is empty
>
> - arch/riscv/kvm/main.c
> module init function, riscv_kvm_init(), calls only kvm_init().
> (*) is empty
>
> Co-developed-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
> arch/mips/kvm/mips.c | 12 +++++++-----
> arch/x86/kvm/vmx/vmx.c | 15 +++++++++++----
> virt/kvm/kvm_main.c | 20 ++++++++++----------
> 3 files changed, 28 insertions(+), 19 deletions(-)
>
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index 092d09fb6a7e..17228584485d 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -1643,11 +1643,6 @@ static int __init kvm_mips_init(void)
> }
>
> ret = kvm_mips_entry_setup();
> - if (ret)
> - return ret;
> -
> - ret = kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);
> -
> if (ret)
> return ret;
>
> @@ -1656,6 +1651,13 @@ static int __init kvm_mips_init(void)
>
> register_die_notifier(&kvm_mips_csr_die_notifier);
>
> + ret = kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);
> +
> + if (ret) {
> + unregister_die_notifier(&kvm_mips_csr_die_notifier);
> + return ret;
> + }
> +
> return 0;
> }
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index e30493fe4553..9bc46c1e64d9 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -8254,6 +8254,15 @@ static void vmx_exit(void)
> }
> module_exit(vmx_exit);
>
> +/* initialize before kvm_init() so that hardware_enable/disable() can work. */
> +static void __init vmx_init_early(void)
> +{
> + int cpu;
> +
> + for_each_possible_cpu(cpu)
> + INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
> +}
> +
> static int __init vmx_init(void)
> {
> int r, cpu;
> @@ -8291,6 +8300,7 @@ static int __init vmx_init(void)
> }
> #endif
>
> + vmx_init_early();
> r = kvm_init(&vmx_init_ops, sizeof(struct vcpu_vmx),
> __alignof__(struct vcpu_vmx), THIS_MODULE);
> if (r)
> @@ -8309,11 +8319,8 @@ static int __init vmx_init(void)
> return r;
> }
>
> - for_each_possible_cpu(cpu) {
> - INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
> -
> + for_each_possible_cpu(cpu)
> pi_init_cpu(cpu);
> - }
>
> #ifdef CONFIG_KEXEC_CORE
> rcu_assign_pointer(crash_vmclear_loaded_vmcss,
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index ec365291c625..0ff03889aa5d 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4883,8 +4883,13 @@ static void hardware_enable_nolock(void *junk)
>
> cpumask_set_cpu(cpu, cpus_hardware_enabled);
>
> + r = kvm_arch_check_processor_compat();
> + if (r)
> + goto out;
> +
> r = kvm_arch_hardware_enable();
>
> +out:
> if (r) {
> cpumask_clear_cpu(cpu, cpus_hardware_enabled);
> atomic_inc(&hardware_enable_failed);
> @@ -5681,11 +5686,6 @@ void kvm_unregister_perf_callbacks(void)
> }
> #endif
>
> -static void check_processor_compat(void *rtn)
> -{
> - *(int *)rtn = kvm_arch_check_processor_compat();
> -}
> -
> int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
> struct module *module)
> {
> @@ -5716,11 +5716,11 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
> if (r < 0)
> goto out_free_1;
>
> - for_each_online_cpu(cpu) {
> - smp_call_function_single(cpu, check_processor_compat, &r, 1);
> - if (r < 0)
> - goto out_free_2;
> - }
> + /* hardware_enable_nolock() checks CPU compatibility on each CPUs. */
> + r = hardware_enable_all();
> + if (r)
> + goto out_free_2;
> + hardware_disable_all();
>
> r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_STARTING, "kvm/cpu:starting",
> kvm_starting_cpu, kvm_dying_cpu);
> --
> 2.25.1
>
Sagi
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