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Subject[PATCH RFC 1/2] KVM: x86: allocate vcpu->arch.cpuid_entries dynamically
Date
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 dynamically. Currenly,
'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 benefits.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/cpuid.c | 55 ++++++++++++++++++++++++---------
arch/x86/kvm/x86.c | 1 +
3 files changed, 42 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5303dbc5c9bc..0c5f2ca3e838 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -636,7 +636,7 @@ 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 3fd6eec202d7..0ce943a8a39a 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -195,6 +195,7 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
{
int r, i;
struct kvm_cpuid_entry *cpuid_entries = NULL;
+ struct kvm_cpuid_entry2 *cpuid_entries2 = NULL;

r = -E2BIG;
if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
@@ -207,31 +208,42 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
r = PTR_ERR(cpuid_entries);
goto out;
}
+ cpuid_entries2 = kvmalloc_array(cpuid->nent, sizeof(cpuid_entries2[0]),
+ GFP_KERNEL_ACCOUNT);
+ if (!cpuid_entries2) {
+ 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;
+ cpuid_entries2[i].function = cpuid_entries[i].function;
+ cpuid_entries2[i].eax = cpuid_entries[i].eax;
+ cpuid_entries2[i].ebx = cpuid_entries[i].ebx;
+ cpuid_entries2[i].ecx = cpuid_entries[i].ecx;
+ cpuid_entries2[i].edx = cpuid_entries[i].edx;
+ cpuid_entries2[i].index = 0;
+ cpuid_entries2[i].flags = 0;
+ cpuid_entries2[i].padding[0] = 0;
+ cpuid_entries2[i].padding[1] = 0;
+ cpuid_entries2[i].padding[2] = 0;
}
+ kvfree(vcpu->arch.cpuid_entries);
+ vcpu->arch.cpuid_entries = cpuid_entries2;
vcpu->arch.cpuid_nent = cpuid->nent;
+
r = kvm_check_cpuid(vcpu);
if (r) {
+ kvfree(vcpu->arch.cpuid_entries);
+ vcpu->arch.cpuid_entries = NULL;
vcpu->arch.cpuid_nent = 0;
- kvfree(cpuid_entries);
- goto out;
+ goto out_free_cpuid;
}

cpuid_fix_nx_cap(vcpu);
kvm_update_cpuid_runtime(vcpu);
kvm_vcpu_after_set_cpuid(vcpu);

+out_free_cpuid:
kvfree(cpuid_entries);
out:
return r;
@@ -241,18 +253,31 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
struct kvm_cpuid2 *cpuid,
struct kvm_cpuid_entry2 __user *entries)
{
+ struct kvm_cpuid_entry2 *cpuid_entries2 = 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;
+
+ if (cpuid->nent) {
+ cpuid_entries2 = vmemdup_user(entries,
+ array_size(sizeof(cpuid_entries2[0]),
+ cpuid->nent));
+ if (IS_ERR(cpuid_entries2)) {
+ r = PTR_ERR(cpuid_entries2);
+ goto out;
+ }
+ }
+ kvfree(vcpu->arch.cpuid_entries);
+ vcpu->arch.cpuid_entries = cpuid_entries2;
vcpu->arch.cpuid_nent = cpuid->nent;
+
r = kvm_check_cpuid(vcpu);
if (r) {
+ kvfree(vcpu->arch.cpuid_entries);
+ vcpu->arch.cpuid_entries = NULL;
vcpu->arch.cpuid_nent = 0;
goto out;
}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1994602a0851..42259a6ec1d8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9610,6 +9610,7 @@ 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);
}
--
2.25.4
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