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authorSean Christopherson <seanjc@google.com>2024-01-09 17:15:32 -0800
committerSean Christopherson <seanjc@google.com>2024-02-06 11:04:11 -0800
commit8284765f03b7a0b18968cefeb5e78aca647b8f8b (patch)
tree2dacd08f38baf749f7a1ca25f490193f88c0008c /virt/kvm
parent422eeb543ac99ea24b80c19492c3359696500a47 (diff)
KVM: Get reference to VM's address space in the async #PF worker
Get a reference to the target VM's address space in async_pf_execute() instead of gifting a reference from kvm_setup_async_pf(). Keeping the address space alive just to service an async #PF is counter-productive, i.e. if the process is exiting and all vCPUs are dead, then NOT doing get_user_pages_remote() and freeing the address space asap is desirable. Handling the mm reference entirely within async_pf_execute() also simplifies the async #PF flows as a whole, e.g. it's not immediately obvious when the worker task vs. the vCPU task is responsible for putting the gifted mm reference. Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> Reviewed-by: Xu Yilun <yilun.xu@intel.com> Link: https://lore.kernel.org/r/20240110011533.503302-4-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'virt/kvm')
-rw-r--r--virt/kvm/async_pf.c32
1 files changed, 18 insertions, 14 deletions
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 85acc9e824b9..628f6df7609f 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -46,8 +46,8 @@ static void async_pf_execute(struct work_struct *work)
{
struct kvm_async_pf *apf =
container_of(work, struct kvm_async_pf, work);
- struct mm_struct *mm = apf->mm;
struct kvm_vcpu *vcpu = apf->vcpu;
+ struct mm_struct *mm = vcpu->kvm->mm;
unsigned long addr = apf->addr;
gpa_t cr2_or_gpa = apf->cr2_or_gpa;
int locked = 1;
@@ -56,16 +56,24 @@ static void async_pf_execute(struct work_struct *work)
might_sleep();
/*
- * This work is run asynchronously to the task which owns
- * mm and might be done in another context, so we must
- * access remotely.
+ * Attempt to pin the VM's host address space, and simply skip gup() if
+ * acquiring a pin fail, i.e. if the process is exiting. Note, KVM
+ * holds a reference to its associated mm_struct until the very end of
+ * kvm_destroy_vm(), i.e. the struct itself won't be freed before this
+ * work item is fully processed.
*/
- mmap_read_lock(mm);
- get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, &locked);
- if (locked)
- mmap_read_unlock(mm);
- mmput(mm);
+ if (mmget_not_zero(mm)) {
+ mmap_read_lock(mm);
+ get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, &locked);
+ if (locked)
+ mmap_read_unlock(mm);
+ mmput(mm);
+ }
+ /*
+ * Notify and kick the vCPU even if faulting in the page failed, e.g.
+ * so that the vCPU can retry the fault synchronously.
+ */
if (IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC))
kvm_arch_async_page_present(vcpu, apf);
@@ -131,10 +139,8 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
#ifdef CONFIG_KVM_ASYNC_PF_SYNC
flush_work(&work->work);
#else
- if (cancel_work_sync(&work->work)) {
- mmput(work->mm);
+ if (cancel_work_sync(&work->work))
kmem_cache_free(async_pf_cache, work);
- }
#endif
spin_lock(&vcpu->async_pf.lock);
}
@@ -205,8 +211,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
work->cr2_or_gpa = cr2_or_gpa;
work->addr = hva;
work->arch = *arch;
- work->mm = current->mm;
- mmget(work->mm);
INIT_WORK(&work->work, async_pf_execute);