-----Original Message-----
From: Will Deacon [mailto:will@kernel.org]
Sent: 03 August 2021 12:39
To: Shameerali Kolothum Thodi <redacted>
Cc: linux-arm-kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
linux-kernel@vger.kernel.org; maz@kernel.org; catalin.marinas@arm.com;
james.morse@arm.com; julien.thierry.kdev@gmail.com;
suzuki.poulose@arm.com; jean-philippe@linaro.org;
Alexandru.Elisei@arm.com; qperret@google.com; Linuxarm
[off-list ref]
Subject: Re: [PATCH v3 1/4] KVM: arm64: Introduce a new VMID allocator for
KVM

On Thu, Jul 29, 2021 at 11:40:06AM +0100, Shameer Kolothum wrote:

quoted

A new VMID allocator for arm64 KVM use. This is based on
arm64 ASID allocator algorithm.

One major deviation from the ASID allocator is the way we
flush the context. Unlike ASID allocator, we expect less
frequent rollover in the case of VMIDs. Hence, instead of
marking the CPU as flush_pending and issuing a local context
invalidation on the next context switch, we broadcast TLB
flush + I-cache invalidation over the inner shareable domain
on rollover.

Signed-off-by: Shameer Kolothum

[off-list ref]

quoted

---

[...]

quoted

+void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
+{
+	unsigned long flags;
+	unsigned int cpu;
+	u64 vmid, old_active_vmid;
+
+	vmid = atomic64_read(&kvm_vmid->id);
+
+	/*
+	 * Please refer comments in check_and_switch_context() in
+	 * arch/arm64/mm/context.c.
+	 */
+	old_active_vmid = atomic64_read(this_cpu_ptr(&active_vmids));
+	if (old_active_vmid && vmid_gen_match(vmid) &&
+	    atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_vmids),
+				     old_active_vmid, vmid))
+		return;
+
+	raw_spin_lock_irqsave(&cpu_vmid_lock, flags);
+
+	/* Check that our VMID belongs to the current generation. */
+	vmid = atomic64_read(&kvm_vmid->id);
+	if (!vmid_gen_match(vmid)) {
+		vmid = new_vmid(kvm_vmid);
+		atomic64_set(&kvm_vmid->id, vmid);

new_vmid() can just set kvm_vmid->id directly

Ok.

quoted

+	}
+
+	cpu = smp_processor_id();

Why?

Left over from previous one. Forgot to remove
as we don't have the tlb_flush_pending check anymore.

Thanks,
Shameer

Will

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