[PATCH] KVM: Relax alignment check for restricted mem

[Isaku Yamahata]

kvm_check_rmem_offset_alignment() only checks based on offset alignment
and GPA alignment.  However, the actual alignment for offset depends
on architecture.  For x86 case, it can be 1G, 2M or 4K.  So even if
GPA is aligned for 1G+, only 1G-alignment is required for offset.

Without this patch, gpa=4G, offset=2G results in failure of memory slot
creation.

Fixes: edc8814b2c77 ("KVM: Require gfn be aligned with restricted offset")
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 15 +++++++++++++++
 virt/kvm/kvm_main.c             |  9 ++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 88e11dd3afde..03af44650f24 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -16,6 +16,7 @@
 #include <linux/irq_work.h>
 #include <linux/irq.h>
 #include <linux/workqueue.h>
+#include <linux/count_zeros.h>
 
 #include <linux/kvm.h>
 #include <linux/kvm_para.h>
@@ -143,6 +144,20 @@
 #define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))
 #define KVM_PAGES_PER_HPAGE(x)	(KVM_HPAGE_SIZE(x) / PAGE_SIZE)
 
+#define kvm_arch_required_alignment	kvm_arch_required_alignment
+static inline int kvm_arch_required_alignment(u64 gpa)
+{
+	int zeros = count_trailing_zeros(gpa);
+
+	WARN_ON_ONCE(!PAGE_ALIGNED(gpa));
+	if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_1G))
+		return KVM_HPAGE_SHIFT(PG_LEVEL_1G);
+	else if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_2M))
+		return KVM_HPAGE_SHIFT(PG_LEVEL_2M);
+
+	return PAGE_SHIFT;
+}
+
 #define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50
 #define KVM_MIN_ALLOC_MMU_PAGES 64UL
 #define KVM_MMU_HASH_SHIFT 12
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c9c4eef457b0..f4ff96171d24 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2113,6 +2113,13 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
 	return false;
 }
 
+#ifndef kvm_arch_required_alignment
+__weak int kvm_arch_required_alignment(u64 gpa)
+{
+	return PAGE_SHIFT
+}
+#endif
+
 /*
  * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
  */
@@ -2123,7 +2130,7 @@ static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
 	if (!gpa)
 		return false;
 
-	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
+	return !!(count_trailing_zeros(offset) >= kvm_arch_required_alignment(gpa));
 }
 
 /*
-- 
2.25.1



-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>