kvm, x86: Properly check whether a pfn is an MMIO or not

pfn_valid check is not sufficient because it only checks if a page has a struct
page or not, if "mem=" was passed to the kernel some valid pages won't have a
struct page. This means that if guests were assigned valid memory that lies
after the mem= boundary it will be passed uncached to the guest no matter what
the guest caching attributes are for this memory.

Introduce a new function e820__mapped_raw_any which is equivalent to
e820__mapped_any but uses the original e820 unmodified and use it to
identify real *RAM*.

Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 20 insertions, 4 deletions

diff --git a/arch/x86/include/asm/e820/api.h b/arch/x86/include/asm/e820/api.h
index 62be73b23d5c..e8f58ddd06d9 100644
--- a/arch/x86/include/asm/e820/api.h
+++ b/arch/x86/include/asm/e820/api.h
@@ -10,6 +10,7 @@ extern struct e820_table *e820_table_firmware;
 
 extern unsigned long pci_mem_start;
 
+extern bool e820__mapped_raw_any(u64 start, u64 end, enum e820_type type);
 extern bool e820__mapped_any(u64 start, u64 end, enum e820_type type);
 extern bool e820__mapped_all(u64 start, u64 end, enum e820_type type);
 
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 2879e234e193..76dd605ee2a3 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -73,12 +73,13 @@ EXPORT_SYMBOL(pci_mem_start);
  * This function checks if any part of the range <start,end> is mapped
  * with type.
  */
-bool e820__mapped_any(u64 start, u64 end, enum e820_type type)
+static bool _e820__mapped_any(struct e820_table *table,
+                              u64 start, u64 end, enum e820_type type)
 {
         int i;
 
-        for (i = 0; i < e820_table->nr_entries; i++) {
-                struct e820_entry *entry = &e820_table->entries[i];
+        for (i = 0; i < table->nr_entries; i++) {
+                struct e820_entry *entry = &table->entries[i];
 
                 if (type && entry->type != type)
                         continue;
@@ -88,6 +89,17 @@ bool e820__mapped_any(u64 start, u64 end, enum e820_type type)
         }
         return 0;
 }
+
+bool e820__mapped_raw_any(u64 start, u64 end, enum e820_type type)
+{
+        return _e820__mapped_any(e820_table_firmware, start, end, type);
+}
+EXPORT_SYMBOL_GPL(e820__mapped_raw_any);
+
+bool e820__mapped_any(u64 start, u64 end, enum e820_type type)
+{
+        return _e820__mapped_any(e820_table, start, end, type);
+}
 EXPORT_SYMBOL_GPL(e820__mapped_any);
 
 /*
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index e10962dfc203..b1f6451022e5 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -44,6 +44,7 @@
 #include <asm/page.h>
 #include <asm/pat.h>
 #include <asm/cmpxchg.h>
+#include <asm/e820/api.h>
 #include <asm/io.h>
 #include <asm/vmx.h>
 #include <asm/kvm_page_track.h>
@@ -2892,7 +2893,9 @@ static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
                          */
                         (!pat_enabled() || pat_pfn_immune_to_uc_mtrr(pfn));
 
-        return true;
+        return !e820__mapped_raw_any(pfn_to_hpa(pfn),
+                                     pfn_to_hpa(pfn + 1) - 1,
+                                     E820_TYPE_RAM);
 }
 
 /* Bits which may be returned by set_spte() */