[PATCH v4 01/15] KVM: Do not restrict the size of KVM-internal memory regions

Claudio Imbrenda
2025-01-23T14:46:38Z

From: Sean Christopherson <seanjc@google.com>

Exempt KVM-internal memslots from the KVM_MEM_MAX_NR_PAGES restriction, as
the limit on the number of pages exists purely to play nice with dirty
bitmap operations, which use 32-bit values to index the bitmaps, and dirty
logging isn't supported for KVM-internal memslots.

Link: https://lore.kernel.org/all/20240802205003.353672-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
---
virt/kvm/kvm_main.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a8a84bf450f9..ee3f040a4891 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1966,7 +1966,15 @@ static int kvm_set_memory_region(struct kvm *kvm,
return -EINVAL;
if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
return -EINVAL;
- if ((mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES)
+
+ /*
+ * The size of userspace-defined memory regions is restricted in order
+ * to play nice with dirty bitmap operations, which are indexed with an
+ * "unsigned int". KVM's internal memory regions don't support dirty
+ * logging, and so are exempt.
+ */
+ if (id < KVM_USER_MEM_SLOTS &&
+ (mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES)
return -EINVAL;

slots = __kvm_memslots(kvm, as_id);
--
2.48.1