Merge tag 'kvm-x86-fixes-6.18-rc2' of https://github.com/kvm-x86/linux into HEAD

KVM x86 fixes for 6.18:

 - Expand the KVM_PRE_FAULT_MEMORY selftest to add a regression test for the
   bug fixed by commit 3ccbf6f470 ("KVM: x86/mmu: Return -EAGAIN if userspace
   deletes/moves memslot during prefault")

 - Don't try to get PMU capabbilities from perf when running a CPU with hybrid
   CPUs/PMUs, as perf will rightly WARN.

 - Rework KVM_CAP_GUEST_MEMFD_MMAP (newly introduced in 6.18) into a more
   generic KVM_CAP_GUEST_MEMFD_FLAGS

 - Add a guest_memfd INIT_SHARED flag and require userspace to explicitly set
   said flag to initialize memory as SHARED, irrespective of MMAP.  The
   behavior merged in 6.18 is that enabling mmap() implicitly initializes
   memory as SHARED, which would result in an ABI collision for x86 CoCo VMs
   as their memory is currently always initialized PRIVATE.

 - Allow mmap() on guest_memfd for x86 CoCo VMs, i.e. on VMs with private
   memory, to enable testing such setups, i.e. to hopefully flush out any
   other lurking ABI issues before 6.18 is officially released.

 - Add testcases to the guest_memfd selftest to cover guest_memfd without MMAP,
   and host userspace accesses to mmap()'d private memory.

include/uapi/linux/kvm.h

@@ -962,7 +962,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_ARM_EL2_E2H0 241
 #define KVM_CAP_RISCV_MP_STATE_RESET 242
 #define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 243
-#define KVM_CAP_GUEST_MEMFD_MMAP 244
+#define KVM_CAP_GUEST_MEMFD_FLAGS 244
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
@@ -1599,7 +1599,8 @@ struct kvm_memory_attributes {
 #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
 
 #define KVM_CREATE_GUEST_MEMFD	_IOWR(KVMIO,  0xd4, struct kvm_create_guest_memfd)
-#define GUEST_MEMFD_FLAG_MMAP	(1ULL << 0)
+#define GUEST_MEMFD_FLAG_MMAP		(1ULL << 0)
+#define GUEST_MEMFD_FLAG_INIT_SHARED	(1ULL << 1)
 
 struct kvm_create_guest_memfd {
 	__u64 size;