Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

[Chao Peng]

On Fri, Jan 13, 2023 at 11:16:27PM +0000, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 9a07380f8d3c..5aefcff614d2 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
> >  		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
> >  			linfo[lpages - 1].disallow_lpage = 1;
> >  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
> > +		if (kvm_slot_can_be_private(slot))
> > +			ugfn |= slot->restricted_offset >> PAGE_SHIFT;
> >  		/*
> >  		 * If the gfn and userspace address are not aligned wrt each
> >  		 * other, disable large page support for this slot.
> 
> Forgot to talk about the bug.  This code needs to handle the scenario where a
> memslot is created with existing, non-uniform attributes.  It might be a bit ugly
> (I didn't even try to write the code), but it's definitely possible, and since
> memslot updates are already slow I think it's best to handle things here.
> 
> In the meantime, I added this so we don't forget to fix it before merging.
> 
> #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> 	pr_crit_once("FIXME: Walk the memory attributes of the slot and set the mixed status appropriately");
> #endif

Here is the code to fix (based on your latest github repo).

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e552374f2357..609ff1cba9c5 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2195,4 +2195,9 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
 	 KVM_X86_QUIRK_FIX_HYPERCALL_INSN |	\
 	 KVM_X86_QUIRK_MWAIT_NEVER_UD_FAULTS)
 
+#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
+void kvm_memory_attributes_create_memslot(struct kvm *kvm,
+					  struct kvm_memory_slot *slot);
+#endif
+
 #endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index eda615f3951c..8833d7201e41 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7201,10 +7201,11 @@ static bool has_mixed_attrs(struct kvm *kvm, struct kvm_memory_slot *slot,
 	return false;
 }
 
-void kvm_arch_set_memory_attributes(struct kvm *kvm,
-				    struct kvm_memory_slot *slot,
-				    unsigned long attrs,
-				    gfn_t start, gfn_t end)
+static void kvm_update_lpage_mixed_flag(struct kvm *kvm,
+					struct kvm_memory_slot *slot,
+					bool set_attrs,
+					unsigned long attrs,
+					gfn_t start, gfn_t end)
 {
 	unsigned long pages, mask;
 	gfn_t gfn, gfn_end, first, last;
@@ -7231,25 +7232,53 @@ void kvm_arch_set_memory_attributes(struct kvm *kvm,
 		first = start & mask;
 		last = (end - 1) & mask;
 
-		/*
-		 * We only need to scan the head and tail page, for middle pages
-		 * we know they will not be mixed.
-		 */
+		/* head page */
 		gfn = max(first, slot->base_gfn);
 		gfn_end = min(first + pages, slot->base_gfn + slot->npages);
+		if(!set_attrs)
+			attrs = kvm_get_memory_attributes(kvm, gfn);
 		mixed = has_mixed_attrs(kvm, slot, level, attrs, gfn, gfn_end);
 		linfo_update_mixed(gfn, slot, level, mixed);
 
 		if (first == last)
 			return;
 
-		for (gfn = first + pages; gfn < last; gfn += pages)
-			linfo_update_mixed(gfn, slot, level, false);
+		/* middle pages */
+		for (gfn = first + pages; gfn < last; gfn += pages) {
+			if (set_attrs) {
+				mixed = false;
+			} else {
+				gfn_end = gfn + pages;
+				attrs = kvm_get_memory_attributes(kvm, gfn);
+				mixed = has_mixed_attrs(kvm, slot, level, attrs,
+							gfn, gfn_end);
+			}
+			linfo_update_mixed(gfn, slot, level, mixed);
+		}
 
+		/* tail page */
 		gfn = last;
 		gfn_end = min(last + pages, slot->base_gfn + slot->npages);
+		if(!set_attrs)
+			attrs = kvm_get_memory_attributes(kvm, gfn);
 		mixed = has_mixed_attrs(kvm, slot, level, attrs, gfn, gfn_end);
 		linfo_update_mixed(gfn, slot, level, mixed);
 	}
 }
+
+void kvm_arch_set_memory_attributes(struct kvm *kvm,
+				    struct kvm_memory_slot *slot,
+				    unsigned long attrs,
+				    gfn_t start, gfn_t end)
+{
+	kvm_update_lpage_mixed_flag(kvm, slot, true, attrs, start, end);
+}
+
+void kvm_memory_attributes_create_memslot(struct kvm *kvm,
+					  struct kvm_memory_slot *slot)
+{
+
+	kvm_update_lpage_mixed_flag(kvm, slot, false, 0, slot->base_gfn,
+				    slot->base_gfn + slot->npages);
+}
 #endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 268c3d16894d..c1074aecf2d0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12443,7 +12443,7 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
 	}
 
 #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
-	pr_crit_once("FIXME: Walk the memory attributes of the slot and set the mixed status appropriately");
+	kvm_memory_attributes_create_memslot(kvm, slot);
 #endif
 
 	if (kvm_page_track_create_memslot(kvm, slot, npages))