On Thu, Mar 10, 2022, Chao Peng wrote:

quoted

@@ -2217,4 +2220,34 @@ static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
 /* Max number of entries allowed for each kvm dirty ring */
 #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
 
+#ifdef CONFIG_MEMFILE_NOTIFIER
+static inline long kvm_memfile_get_pfn(struct kvm_memory_slot *slot, gfn_t gfn,
+				       int *order)
+{
+	pgoff_t index = gfn - slot->base_gfn +
+			(slot->private_offset >> PAGE_SHIFT);

This is broken for 32-bit kernels, where gfn_t is a 64-bit value but pgoff_t is a
32-bit value.  There's no reason to support this for 32-bit kernels, so...

The easiest fix, and likely most maintainable for other code too, would be to
add a dedicated CONFIG for private memory, and then have KVM check that for all
the memfile stuff.  x86 can then select it only for 64-bit kernels, and in turn
select MEMFILE_NOTIFIER iff private memory is supported.

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index ca7b2a6a452a..ee9c8c155300 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig

@@ -48,7 +48,9 @@ config KVM
        select SRCU
        select INTERVAL_TREE
        select HAVE_KVM_PM_NOTIFIER if PM
-       select MEMFILE_NOTIFIER
+       select HAVE_KVM_PRIVATE_MEM if X86_64
+       select MEMFILE_NOTIFIER if HAVE_KVM_PRIVATE_MEM
+
        help
          Support hosting fully virtualized guest machines using hardware
          virtualization extensions.  You will need a fairly recent

And in addition to replacing checks on CONFIG_MEMFILE_NOTIFIER, the probing of
whether or not KVM_MEM_PRIVATE is allowed can be:

@@ -1499,23 +1499,19 @@ static void kvm_replace_memslot(struct kvm *kvm,
        }
 }

-bool __weak kvm_arch_private_memory_supported(struct kvm *kvm)
-{
-       return false;
-}
-
 static int check_memory_region_flags(struct kvm *kvm,
                                const struct kvm_userspace_memory_region *mem)
 {
        u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;

-       if (kvm_arch_private_memory_supported(kvm))
-               valid_flags |= KVM_MEM_PRIVATE;
-
 #ifdef __KVM_HAVE_READONLY_MEM
        valid_flags |= KVM_MEM_READONLY;
 #endif

+#ifdef CONFIG_KVM_HAVE_PRIVATE_MEM
+       valid_flags |= KVM_MEM_PRIVATE;
+#endif