[13/18] KVM: x86/mmu: Avoid warning when installing non-private memory attributes

Commit Message

Nicolas Saenz Julienne June 9, 2024, 3:49 p.m. UTC

In preparation to introducing RWX memory attributes, make sure
user-space is attempting to install a memory attribute with
KVM_MEMORY_ATTRIBUTE_PRIVATE before throwing a warning on systems with
no private memory support.

Signed-off-by: Nicolas Saenz Julienne <[e-mail]>
---
 arch/x86/kvm/mmu/mmu.c | 8 ++++++--
 virt/kvm/kvm_main.c    | 1 +
 2 files changed, 7 insertions(+), 2 deletions(-)

Comments

Sean Christopherson Sept. 13, 2024, 7:13 p.m. UTC | #1

On Sun, Jun 09, 2024, Nicolas Saenz Julienne wrote:
> In preparation to introducing RWX memory attributes, make sure
> user-space is attempting to install a memory attribute with
> KVM_MEMORY_ATTRIBUTE_PRIVATE before throwing a warning on systems with
> no private memory support.
> 
> Signed-off-by: Nicolas Saenz Julienne <[e-mail]>
> ---
>  arch/x86/kvm/mmu/mmu.c | 8 ++++++--
>  virt/kvm/kvm_main.c    | 1 +
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index b0c210b96419f..d56c04fbdc66b 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -7359,6 +7359,9 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
>  bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm,
>  					struct kvm_gfn_range *range)
>  {
> +	unsigned long attrs = range->arg.attributes;
> +	bool priv_attr = attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;

It's probably worth making this check generic straightaway, e.g. build and then
check the set of allowed attributes, similar to how check_memory_region_flags()
builds and checks the set of allowed flags.

Patch

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b0c210b96419f..d56c04fbdc66b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7359,6 +7359,9 @@  void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
 bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm,
 					struct kvm_gfn_range *range)
 {
+	unsigned long attrs = range->arg.attributes;
+	bool priv_attr = attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;
+
 	/*
 	 * Zap SPTEs even if the slot can't be mapped PRIVATE.  KVM x86 only
 	 * supports KVM_MEMORY_ATTRIBUTE_PRIVATE, and so it *seems* like KVM
@@ -7370,7 +7373,7 @@  bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm,
 	 * Zapping SPTEs in this case ensures KVM will reassess whether or not
 	 * a hugepage can be used for affected ranges.
 	 */
-	if (WARN_ON_ONCE(!kvm_arch_has_private_mem(kvm)))
+	if (WARN_ON_ONCE(priv_attr && !kvm_arch_has_private_mem(kvm)))
 		return false;
 
 	return kvm_unmap_gfn_range(kvm, range);
@@ -7415,6 +7418,7 @@  bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
 					 struct kvm_gfn_range *range)
 {
 	unsigned long attrs = range->arg.attributes;
+	bool priv_attr = attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;
 	struct kvm_memory_slot *slot = range->slot;
 	int level;
 
@@ -7427,7 +7431,7 @@  bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
 	 * a range that has PRIVATE GFNs, and conversely converting a range to
 	 * SHARED may now allow hugepages.
 	 */
-	if (WARN_ON_ONCE(!kvm_arch_has_private_mem(kvm)))
+	if (WARN_ON_ONCE(priv_attr && !kvm_arch_has_private_mem(kvm)))
 		return false;
 
 	/*
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 14841acb8b959..63c4b6739edee 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2506,6 +2506,7 @@  static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
 	struct kvm_mmu_notifier_range pre_set_range = {
 		.start = start,
 		.end = end,
+		.arg.attributes = attributes,
 		.handler = kvm_pre_set_memory_attributes,
 		.on_lock = kvm_mmu_invalidate_begin,
 		.flush_on_ret = true,