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Message-ID: <a99c92d1ed04744d0829b79ff2286348fac8a420.camel@redhat.com>
Date: Mon, 05 Oct 2020 13:11:08 +0300
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <sean.j.christopherson@...el.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
"Dr . David Alan Gilbert" <dgilbert@...hat.com>,
Wei Huang <whuang2@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] KVM: x86: allocate vcpu->arch.cpuid_entries
dynamically
On Thu, 2020-10-01 at 15:05 +0200, Vitaly Kuznetsov wrote:
> The current limit for guest CPUID leaves (KVM_MAX_CPUID_ENTRIES, 80)
> is reported to be insufficient but before we bump it let's switch to
> allocating vcpu->arch.cpuid_entries[] array dynamically. Currently,
> 'struct kvm_cpuid_entry2' is 40 bytes so vcpu->arch.cpuid_entries is
> 3200 bytes which accounts for 1/4 of the whole 'struct kvm_vcpu_arch'
> but having it pre-allocated (for all vCPUs which we also pre-allocate)
> gives us no real benefits.
>
> Another plus of the dynamic allocation is that we now do kvm_check_cpuid()
> check before we assign anything to vcpu->arch.cpuid_nent/cpuid_entries so
> no changes are made in case the check fails.
>
> Opportunistically remove unneeded 'out' labels from
> kvm_vcpu_ioctl_set_cpuid()/kvm_vcpu_ioctl_set_cpuid2() and return
> directly whenever possible.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
> arch/x86/include/asm/kvm_host.h | 2 +-
> arch/x86/kvm/cpuid.c | 89 +++++++++++++++++++--------------
> arch/x86/kvm/x86.c | 1 +
> 3 files changed, 53 insertions(+), 39 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index d0f77235da92..7d259e21ea04 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -637,7 +637,7 @@ struct kvm_vcpu_arch {
> int halt_request; /* real mode on Intel only */
>
> int cpuid_nent;
> - struct kvm_cpuid_entry2 cpuid_entries[KVM_MAX_CPUID_ENTRIES];
> + struct kvm_cpuid_entry2 *cpuid_entries;
>
> int maxphyaddr;
> int max_tdp_level;
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 529348ddedc1..3fe20c4da0a6 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -210,46 +210,53 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
> struct kvm_cpuid_entry __user *entries)
> {
> int r, i;
> - struct kvm_cpuid_entry *cpuid_entries = NULL;
> + struct kvm_cpuid_entry *e = NULL;
> + struct kvm_cpuid_entry2 *e2 = NULL;
>
> - r = -E2BIG;
> if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
> - goto out;
> + return -E2BIG;
> +
> if (cpuid->nent) {
> - cpuid_entries = vmemdup_user(entries,
> - array_size(sizeof(struct kvm_cpuid_entry),
> - cpuid->nent));
> - if (IS_ERR(cpuid_entries)) {
> - r = PTR_ERR(cpuid_entries);
> - goto out;
> + e = vmemdup_user(entries, array_size(sizeof(*e), cpuid->nent));
> + if (IS_ERR(e))
> + return PTR_ERR(e);
> +
> + e2 = kvmalloc_array(cpuid->nent, sizeof(*e2), GFP_KERNEL_ACCOUNT);
> + if (!e2) {
> + r = -ENOMEM;
> + goto out_free_cpuid;
> }
> }
> for (i = 0; i < cpuid->nent; i++) {
> - vcpu->arch.cpuid_entries[i].function = cpuid_entries[i].function;
> - vcpu->arch.cpuid_entries[i].eax = cpuid_entries[i].eax;
> - vcpu->arch.cpuid_entries[i].ebx = cpuid_entries[i].ebx;
> - vcpu->arch.cpuid_entries[i].ecx = cpuid_entries[i].ecx;
> - vcpu->arch.cpuid_entries[i].edx = cpuid_entries[i].edx;
> - vcpu->arch.cpuid_entries[i].index = 0;
> - vcpu->arch.cpuid_entries[i].flags = 0;
> - vcpu->arch.cpuid_entries[i].padding[0] = 0;
> - vcpu->arch.cpuid_entries[i].padding[1] = 0;
> - vcpu->arch.cpuid_entries[i].padding[2] = 0;
> + e2[i].function = e[i].function;
> + e2[i].eax = e[i].eax;
> + e2[i].ebx = e[i].ebx;
> + e2[i].ecx = e[i].ecx;
> + e2[i].edx = e[i].edx;
> + e2[i].index = 0;
> + e2[i].flags = 0;
> + e2[i].padding[0] = 0;
> + e2[i].padding[1] = 0;
> + e2[i].padding[2] = 0;
> }
> - vcpu->arch.cpuid_nent = cpuid->nent;
> - r = kvm_check_cpuid(vcpu->arch.cpuid_entries, cpuid->nent);
> +
> + r = kvm_check_cpuid(e2, cpuid->nent);
> if (r) {
> - vcpu->arch.cpuid_nent = 0;
> - kvfree(cpuid_entries);
> - goto out;
> + kvfree(e2);
> + goto out_free_cpuid;
> }
>
> + kvfree(vcpu->arch.cpuid_entries);
> + vcpu->arch.cpuid_entries = e2;
> + vcpu->arch.cpuid_nent = cpuid->nent;
> +
> cpuid_fix_nx_cap(vcpu);
> kvm_update_cpuid_runtime(vcpu);
> kvm_vcpu_after_set_cpuid(vcpu);
>
> - kvfree(cpuid_entries);
> -out:
> +out_free_cpuid:
> + kvfree(e);
> +
> return r;
> }
>
> @@ -257,26 +264,32 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
> struct kvm_cpuid2 *cpuid,
> struct kvm_cpuid_entry2 __user *entries)
> {
> + struct kvm_cpuid_entry2 *e2 = NULL;
> int r;
>
> - r = -E2BIG;
> if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
> - goto out;
> - r = -EFAULT;
> - if (copy_from_user(&vcpu->arch.cpuid_entries, entries,
> - cpuid->nent * sizeof(struct kvm_cpuid_entry2)))
> - goto out;
> - vcpu->arch.cpuid_nent = cpuid->nent;
> - r = kvm_check_cpuid(vcpu->arch.cpuid_entries, cpuid->nent);
> + return -E2BIG;
> +
> + if (cpuid->nent) {
> + e2 = vmemdup_user(entries, array_size(sizeof(*e2), cpuid->nent));
> + if (IS_ERR(e2))
> + return PTR_ERR(e2);
> + }
> +
> + r = kvm_check_cpuid(e2, cpuid->nent);
> if (r) {
> - vcpu->arch.cpuid_nent = 0;
> - goto out;
> + kvfree(e2);
> + return r;
> }
>
> + kvfree(vcpu->arch.cpuid_entries);
> + vcpu->arch.cpuid_entries = e2;
> + vcpu->arch.cpuid_nent = cpuid->nent;
> +
> kvm_update_cpuid_runtime(vcpu);
> kvm_vcpu_after_set_cpuid(vcpu);
> -out:
> - return r;
> +
> + return 0;
> }
>
> int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c4015a43cc8a..f8ed1bde18af 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9877,6 +9877,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
> kvm_mmu_destroy(vcpu);
> srcu_read_unlock(&vcpu->kvm->srcu, idx);
> free_page((unsigned long)vcpu->arch.pio_data);
> + kvfree(vcpu->arch.cpuid_entries);
> if (!lapic_in_kernel(vcpu))
> static_key_slow_dec(&kvm_no_apic_vcpu);
> }
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Best regards,
Maxim Levitsky
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