[SRU][J/allwinner-5.17][J/starfive-5.17][PATCH v2 1/1] RISC-V: KVM: Fix SRCU deadlock caused by kvm_riscv_check_vcpu_requests()

[Emil Renner Berthing]

From: Anup Patel <apatel at ventanamicro.com>

BugLink: https://bugs.launchpad.net/bugs/1980594

The kvm_riscv_check_vcpu_requests() is called with SRCU read lock held
and for KVM_REQ_SLEEP request it will block the VCPU without releasing
SRCU read lock. This causes KVM ioctls (such as KVM_IOEVENTFD) from
other VCPUs of the same Guest/VM to hang/deadlock if there is any
synchronize_srcu() or synchronize_srcu_expedited() in the path.

To fix the above in kvm_riscv_check_vcpu_requests(), we should do SRCU
read unlock before blocking the VCPU and do SRCU read lock after VCPU
wakeup.

Fixes: cce69aff689e ("RISC-V: KVM: Implement VCPU interrupts and requests handling")
Reported-by: Bin Meng <bmeng.cn at gmail.com>
Signed-off-by: Anup Patel <apatel at ventanamicro.com>
Reviewed-by: Atish Patra <atishp at rivosinc.com>
Tested-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
Tested-by: Bin Meng <bmeng.cn at gmail.com>
Signed-off-by: Anup Patel <anup at brainfault.org>
(backported from commit be82abe6a76ba8e76f25312566182b0f13c4fbf9)
[esmil: open code the srcu lock/unlock that now has static inline wrappers]
Signed-off-by: Emil Renner Berthing <emil.renner.berthing at canonical.com>
---
 arch/riscv/kvm/vcpu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index aad430668bb4..5c00a6526dca 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -673,9 +673,11 @@ static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
 
 	if (kvm_request_pending(vcpu)) {
 		if (kvm_check_request(KVM_REQ_SLEEP, vcpu)) {
+			srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
 			rcuwait_wait_event(wait,
 				(!vcpu->arch.power_off) && (!vcpu->arch.pause),
 				TASK_INTERRUPTIBLE);
+			vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
 
 			if (vcpu->arch.power_off || vcpu->arch.pause) {
 				/*
-- 
2.36.1