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Subject[PATCH v6 14/14] kvm, x86: Properly check whether a pfn is an MMIO or not
Date
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>
---
v1 -> v2:
- Introduce e820__mapped_raw_any
---
arch/x86/include/asm/e820/api.h | 1 +
arch/x86/kernel/e820.c | 18 +++++++++++++++---
arch/x86/kvm/mmu.c | 5 ++++-
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 4562062..b3f6e89 100644
--- a/arch/x86/include/asm/e820/api.h
+++ b/arch/x86/include/asm/e820/api.h
@@ -12,6 +12,7 @@ extern unsigned long e820_saved_max_low_pfn;

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 ef914d0..3039659 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -75,12 +75,13 @@ 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;
@@ -90,6 +91,17 @@ 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 da9c423..abf6a0d 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>
@@ -2875,7 +2876,9 @@ 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() */
--
2.7.4
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