[patch, try#2] kvm: fix GFP_KERNEL allocation in atomic section in kvm_dev_ioctl_create_vcpu()

* Ingo Molnar <mingo@xxxxxxx> wrote:

> > Yes it does.  It calls nonpaging_init_context() which calls 
> > vmx_set_cr3() which promptly trashes address space of the VM that 
> > previously ran on that vcpu (or, if there were none, logs a vmwrite 
> > error).
> 
> ok, i missed that. Nevertheless the problem of the nonatomic alloc 
> remains. I guess a kvm_mmu_init() needs to be split into 
> kvm_mmu_create() and kvm_mmu_setup()?

the patch below implements this fix. Lightly tested on 32-bit/VMX on 
2.6.20-rc2-rt2 but seems to have done the trick.

        Ingo

-------------------->
Subject: [patch] kvm: fix GFP_KERNEL allocation in atomic section in 
kvm_dev_ioctl_create_vcpu()
From: Ingo Molnar <mingo@xxxxxxx>

fix an GFP_KERNEL allocation in atomic section: 
kvm_dev_ioctl_create_vcpu() called kvm_mmu_init(), which calls 
alloc_pages(), while holding the vcpu.

The fix is to set up the MMU state in two phases: kvm_mmu_create() and 
kvm_mmu_setup().

(NOTE: free_vcpus does an kvm_mmu_destroy() call so there's no need
 for any extra teardown branch on allocation/init failure here.)

Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 drivers/kvm/kvm.h      |    3 ++-
 drivers/kvm/kvm_main.c |   10 ++++++----
 drivers/kvm/mmu.c      |   24 +++++++++---------------
 3 files changed, 17 insertions(+), 20 deletions(-)

Index: linux/drivers/kvm/kvm.h
===================================================================
--- linux.orig/drivers/kvm/kvm.h
+++ linux/drivers/kvm/kvm.h
@@ -319,7 +319,8 @@ int kvm_init_arch(struct kvm_arch_ops *o
 void kvm_exit_arch(void);
 
 void kvm_mmu_destroy(struct kvm_vcpu *vcpu);
-int kvm_mmu_init(struct kvm_vcpu *vcpu);
+int kvm_mmu_create(struct kvm_vcpu *vcpu);
+int kvm_mmu_setup(struct kvm_vcpu *vcpu);
 
 int kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
 void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
Index: linux/drivers/kvm/kvm_main.c
===================================================================
--- linux.orig/drivers/kvm/kvm_main.c
+++ linux/drivers/kvm/kvm_main.c
@@ -522,12 +522,14 @@ static int kvm_dev_ioctl_create_vcpu(str
        if (r < 0)
                goto out_free_vcpus;
 
-       kvm_arch_ops->vcpu_load(vcpu);
+       r = kvm_mmu_create(vcpu);
+       if (r < 0)
+               goto out_free_vcpus;
 
-       r = kvm_arch_ops->vcpu_setup(vcpu);
+       kvm_arch_ops->vcpu_load(vcpu);
+       r = kvm_mmu_setup(vcpu);
        if (r >= 0)
-               r = kvm_mmu_init(vcpu);
-
+               r = kvm_arch_ops->vcpu_setup(vcpu);
        vcpu_put(vcpu);
 
        if (r < 0)
Index: linux/drivers/kvm/mmu.c
===================================================================
--- linux.orig/drivers/kvm/mmu.c
+++ linux/drivers/kvm/mmu.c
@@ -639,28 +639,22 @@ error_1:
        return -ENOMEM;
 }
 
-int kvm_mmu_init(struct kvm_vcpu *vcpu)
+int kvm_mmu_create(struct kvm_vcpu *vcpu)
 {
-       int r;
-
        ASSERT(vcpu);
        ASSERT(!VALID_PAGE(vcpu->mmu.root_hpa));
        ASSERT(list_empty(&vcpu->free_pages));
 
-       r = alloc_mmu_pages(vcpu);
-       if (r)
-               goto out;
-
-       r = init_kvm_mmu(vcpu);
-       if (r)
-               goto out_free_pages;
+       return alloc_mmu_pages(vcpu);
+}
 
-       return 0;
+int kvm_mmu_setup(struct kvm_vcpu *vcpu)
+{
+       ASSERT(vcpu);
+       ASSERT(!VALID_PAGE(vcpu->mmu.root_hpa));
+       ASSERT(!list_empty(&vcpu->free_pages));
 
-out_free_pages:
-       free_mmu_pages(vcpu);
-out:
-       return r;
+       return init_kvm_mmu(vcpu);
 }
 
 void kvm_mmu_destroy(struct kvm_vcpu *vcpu)

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