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))