linux-kernel - [PATCH 2/4] KVM: Put mm immediately after async #PF worker completes remote gup()

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Date: Tue,  9 Jan 2024 17:15:31 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	David Matlack <dmatlack@...gle.com>, Xu Yilun <yilun.xu@...ux.intel.com>, 
	Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH 2/4] KVM: Put mm immediately after async #PF worker completes
 remote gup()

Put the async #PF worker's reference to the VM's address space as soon as
the worker is done with the mm.  This will allow deferring getting a
reference to the worker itself without having to track whether or not
getting a reference succeeded.

Note, if the vCPU is still alive, there is no danger of the worker getting
stuck with tearing down the host page tables, as userspace also holds a
reference (obviously), i.e. there is no risk of delaying the page-present
notification due to triggering the slow path in mmput().

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 virt/kvm/async_pf.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 876927a558ad..d5dc50318aa6 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -64,6 +64,7 @@ static void async_pf_execute(struct work_struct *work)
 	get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, &locked);
 	if (locked)
 		mmap_read_unlock(mm);
+	mmput(mm);
 
 	if (IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC))
 		kvm_arch_async_page_present(vcpu, apf);
@@ -85,8 +86,6 @@ static void async_pf_execute(struct work_struct *work)
 	trace_kvm_async_pf_completed(addr, cr2_or_gpa);
 
 	__kvm_vcpu_wake_up(vcpu);
-
-	mmput(mm);
 }
 
 static void kvm_flush_and_free_async_pf_work(struct kvm_async_pf *work)
-- 
2.43.0.472.g3155946c3a-goog