On 08/02/18 11:01, Christoffer Dall wrote:
On Tue, Jan 09, 2018 at 07:04:04PM +0000, Suzuki K Poulose wrote:
We allocate the entry level page tables for stage2 when the
VM is created. This doesn't give us the flexibility of configuring
the physical address space size for a VM. In order to allow
the VM to choose the required size, we delay the allocation of
stage2 entry level tables until we really try to map something.

This could be either when the VM creates a memory range or when
it tries to map a device memory. So we add in a hook to these
two places to make sure the tables are allocated. We use
kvm->slots_lock to serialize the allocation entry point, since
we add hooks to the arch specific call back with the mutex held.


- * kvm_phys_addr_ioremap - map a device range to guest IPA
- *
- * @kvm:       The KVM pointer
- * @guest_ipa: The IPA at which to insert the mapping
- * @pa:                The physical address of the device
- * @size:      The size of the mapping
+ * Finalise the stage2 page table layout. Must be called with kvm->slots_lock
+ * held.
-int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
+static int __kvm_init_stage2_table(struct kvm *kvm)
+       /* Double check if somebody has already allocated it */

dubious comment: Either leave it out or explain that we need to check
again with the mutex held.

+       if (likely(kvm->arch.pgd))
+               return 0;
+       return kvm_alloc_stage2_pgd(kvm);
+static int kvm_init_stage2_table(struct kvm *kvm)
+       int rc;
+       /*
+        * Once allocated, the stage2 entry level tables are only
+        * freed when the KVM instance is destroyed. So, if we see
+        * something valid here, that guarantees that we have
+        * done the one time allocation and it is something valid
+        * and won't go away until the last reference to the KVM
+        * is gone.
+        */

Really not sure if this comment adds something beyond what's described
by the code already?

Agreed. Will clean it up.



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