[PATCH 1/2] KVM: MMU: Fix infinite loop when there is no available mmu page

[Wanpeng Li]

From: Wanpeng Li <wanpeng...@hotmail.com>

The below test case can cause infinite loop in kvm when ept=0.

    #include <unistd.h>
    #include <sys/syscall.h>
    #include <string.h>
    #include <stdint.h>
    #include <linux/kvm.h>
    #include <fcntl.h>
    #include <sys/ioctl.h>
    
    long r[5];
    int main()
    {
        r[2] = open("/dev/kvm", O_RDONLY);
        r[3] = ioctl(r[2], KVM_CREATE_VM, 0);
        r[4] = ioctl(r[3], KVM_CREATE_VCPU, 7);
        ioctl(r[4], KVM_RUN, 0);
    }

It doesn't setup the memory regions, mmu_alloc_shadow/direct_roots() in 
kvm return 1 when kvm fails to allocate root page table which can result 
in beblow infinite loop:

    vcpu_run() {
        for (;;) {
                r = vcpu_enter_guest()::kvm_mmu_reload() returns 1 
                if (r <= 0)
                        break;
                if (need_resched())
                        cond_resched();
      }
    }

This patch fixes it by returning -ENOSPC when there is no available kvm mmu 
page for root page table.

Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Radim Krčmář <rkrc...@redhat.com>
Fixes: 26eeb53cf0f (KVM: MMU: Bail out immediately if there is no available mmu 
page)
Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com>
---
 arch/x86/kvm/mmu.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c9aaa18..89da688 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3395,7 +3395,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
                spin_lock(&vcpu->kvm->mmu_lock);
                if(make_mmu_pages_available(vcpu) < 0) {
                        spin_unlock(&vcpu->kvm->mmu_lock);
-                       return 1;
+                       return -ENOSPC;
                }
                sp = kvm_mmu_get_page(vcpu, 0, 0,
                                vcpu->arch.mmu.shadow_root_level, 1, ACC_ALL);
@@ -3410,7 +3410,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
                        spin_lock(&vcpu->kvm->mmu_lock);
                        if (make_mmu_pages_available(vcpu) < 0) {
                                spin_unlock(&vcpu->kvm->mmu_lock);
-                               return 1;
+                               return -ENOSPC;
                        }
                        sp = kvm_mmu_get_page(vcpu, i << (30 - PAGE_SHIFT),
                                        i << 30, PT32_ROOT_LEVEL, 1, ACC_ALL);
@@ -3450,7 +3450,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
                spin_lock(&vcpu->kvm->mmu_lock);
                if (make_mmu_pages_available(vcpu) < 0) {
                        spin_unlock(&vcpu->kvm->mmu_lock);
-                       return 1;
+                       return -ENOSPC;
                }
                sp = kvm_mmu_get_page(vcpu, root_gfn, 0,
                                vcpu->arch.mmu.shadow_root_level, 0, ACC_ALL);
@@ -3487,7 +3487,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
                spin_lock(&vcpu->kvm->mmu_lock);
                if (make_mmu_pages_available(vcpu) < 0) {
                        spin_unlock(&vcpu->kvm->mmu_lock);
-                       return 1;
+                       return -ENOSPC;
                }
                sp = kvm_mmu_get_page(vcpu, root_gfn, i << 30, PT32_ROOT_LEVEL,
                                      0, ACC_ALL);
-- 
2.7.4