kvm: x86: Dynamically allocate guest_fpu

Previously, the guest_fpu field was embedded in the kvm_vcpu_arch
struct. Unfortunately, the field is quite large, (e.g., 4352 bytes on my
current setup). This bloats the kvm_vcpu_arch struct for x86 into an
order 3 memory allocation, which can become a problem on overcommitted
machines. Thus, this patch moves the fpu state outside of the
kvm_vcpu_arch struct.

With this patch applied, the kvm_vcpu_arch struct is reduced to 15168
bytes for vmx on my setup when building the kernel with kvmconfig.

Suggested-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Marc Orr <marcorr@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c3461f835445..b8fa74ce3af2 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6349,6 +6349,7 @@ static void vmx_free_vcpu(struct kvm_vcpu *vcpu)
 	free_loaded_vmcs(vmx->loaded_vmcs);
 	kfree(vmx->guest_msrs);
 	kvm_vcpu_uninit(vcpu);
+	kmem_cache_free(x86_fpu_cache, vmx->vcpu.arch.guest_fpu);
 	kmem_cache_free(kvm_vcpu_cache, vmx);
 }
 
@@ -6362,6 +6363,13 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 	if (!vmx)
 		return ERR_PTR(-ENOMEM);
 
+	vmx->vcpu.arch.guest_fpu = kmem_cache_zalloc(x86_fpu_cache, GFP_KERNEL);
+	if (!vmx->vcpu.arch.guest_fpu) {
+		printk(KERN_ERR "kvm: failed to allocate vcpu's fpu\n");
+		err = -ENOMEM;
+		goto free_partial_vcpu;
+	}
+
 	vmx->vpid = allocate_vpid();
 
 	err = kvm_vcpu_init(&vmx->vcpu, kvm, id);
@@ -6454,6 +6462,8 @@ uninit_vcpu:
 	kvm_vcpu_uninit(&vmx->vcpu);
 free_vcpu:
 	free_vpid(vmx->vpid);
+	kmem_cache_free(x86_fpu_cache, vmx->vcpu.arch.guest_fpu);
+free_partial_vcpu:
 	kmem_cache_free(kvm_vcpu_cache, vmx);
 	return ERR_PTR(err);
 }