Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes
From: Sean Christopherson <seanjc@google.com>
Date: 2023-01-13 22:02:36
Also in:
kvm, linux-arch, linux-doc, linux-fsdevel, linux-mm, lkml, qemu-devel
On Fri, Dec 02, 2022, Chao Peng wrote:
quoted hunk ↗ jump to hunk
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig index fbeaa9ddef59..a8e379a3afee 100644 --- a/arch/x86/kvm/Kconfig +++ b/arch/x86/kvm/Kconfig@@ -49,6 +49,7 @@ config KVM select SRCU select INTERVAL_TREE select HAVE_KVM_PM_NOTIFIER if PM + select HAVE_KVM_MEMORY_ATTRIBUTES
I would prefer to call this KVM_GENERIC_MEMORY_ATTRIBUTES. Similar to KVM_GENERIC_HARDWARE_ENABLING, ARM does need/have hardware enabling, it just doesn't want KVM's generic implementation. In this case, pKVM does support memory attributes, but uses stage-2 tables to track ownership and doesn't need/want the overhead of the generic implementation.
help
...
+#define KVM_MEMORY_ATTRIBUTE_READ (1ULL << 0) +#define KVM_MEMORY_ATTRIBUTE_WRITE (1ULL << 1) +#define KVM_MEMORY_ATTRIBUTE_EXECUTE (1ULL << 2) +#define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3)
I think we should carve out bits 0-2 for RWX, but I don't think we should actually define them until they're actually accepted by KVM.
+static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
+ struct kvm_memory_attributes *attrs)
+{
+ gfn_t start, end;
+ unsigned long i;
+ void *entry;
+ u64 supported_attrs = kvm_supported_mem_attributes(kvm);
+
+ /* flags is currently not used. */
+ if (attrs->flags)
+ return -EINVAL;
+ if (attrs->attributes & ~supported_attrs)Nit, no need for "supported_attrs", just consume kvm_supported_mem_attributes() directly.
+ return -EINVAL; + if (attrs->size == 0 || attrs->address + attrs->size < attrs->address) + return -EINVAL; + if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size)) + return -EINVAL; + + start = attrs->address >> PAGE_SHIFT; + end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT; + + entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL; + + mutex_lock(&kvm->lock);
Peeking forward multiple patches, this needs to take kvm->slots_lock, not kvm->lock. There's a bug in the lpage_disallowed patch that I believe can most easily be solved by making this mutually exclusive with memslot changes. When a memslot is created, KVM needs to walk through the attributes to detect whether or not the attributes are identical for the entire slot. To avoid races, that means taking slots_lock. The alternative would be to query the attributes when adjusting the hugepage level and avoid lpage_disallowed entirely, but in the (very brief) time I've thought about this I haven't come up with a way to do that in a performant manner.
+ for (i = start; i < end; i++)
Curly braces needed on the for-loop.