Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Chao Peng]

On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
... 
> Strongly prefer to use similar logic to existing code that detects wraps:
> 
>               mem->restricted_offset + mem->memory_size < 
> mem->restricted_offset
> 
> This is also where I'd like to add the "gfn is aligned to offset" check, 
> though
> my brain is too fried to figure that out right now.

Used count_trailing_zeros() for this TODO, unsure we have other better
approach.

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index afc8c26fa652..fd34c5f7cd2f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -56,6 +56,7 @@
 #include <asm/processor.h>
 #include <asm/ioctl.h>
 #include <linux/uaccess.h>
+#include <linux/count_zeros.h>
 
 #include "coalesced_mmio.h"
 #include "async_pf.h"
@@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct 
kvm_memslots *slots, int id,
        return false;
 }
 
+/*
+ * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
+ */
+static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
+{
+       if (!offset)
+               return true;
+       if (!gpa)
+               return false;
+
+       return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -2128,7 +2142,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
        if (mem->flags & KVM_MEM_PRIVATE &&
            (mem->restrictedmem_offset & (PAGE_SIZE - 1) ||
             mem->restrictedmem_offset + mem->memory_size < 
mem->restrictedmem_offset ||
-            0 /* TODO: require gfn be aligned with restricted offset */))
+            !kvm_check_rmem_offset_alignment(mem->restrictedmem_offset,
+                                             mem->guest_phys_addr)))
                return -EINVAL;
        if (as_id >= kvm_arch_nr_memslot_as_ids(kvm) || id >= KVM_MEM_SLOTS_NUM)
                return -EINVAL;