[PATCHv2 22/29] x86/tdx: Make pages shared in ioremap()

Kirill A. Shutemov
2022-01-24T15:03:03Z

In TDX guests, guest memory is protected from host access. If a guest
performs I/O, it needs to explicitly share the I/O memory with the host.

Make all ioremap()ed pages that are not backed by normal memory
(IORES_DESC_NONE or IORES_DESC_RESERVED) mapped as shared.

Since TDX memory encryption support is similar to AMD SEV architecture,
reuse the infrastructure from AMD SEV code.

Add tdx_shared_mask() interface to get the TDX guest shared bitmask.

pgprot_decrypted() is used by drivers (i915, virtio_gpu, vfio). Export
both pgprot_encrypted() and pgprot_decrypted().

Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/include/asm/pgtable.h | 19 +++++++++++++------
arch/x86/include/asm/tdx.h | 4 ++++
arch/x86/kernel/cc_platform.c | 23 +++++++++++++++++++++++
arch/x86/kernel/tdx.c | 9 +++++++++
arch/x86/mm/ioremap.c | 5 +++++
5 files changed, 54 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 8a9432fb3802..40e22db48319 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -15,12 +15,6 @@
cachemode2protval(_PAGE_CACHE_MODE_UC_MINUS))) \
: (prot))

-/*
- * Macros to add or remove encryption attribute
- */
-#define pgprot_encrypted(prot) __pgprot(__sme_set(pgprot_val(prot)))
-#define pgprot_decrypted(prot) __pgprot(__sme_clr(pgprot_val(prot)))
-
#ifndef __ASSEMBLY__
#include <linux/spinlock.h>
#include <asm/x86_init.h>
@@ -38,6 +32,19 @@ void ptdump_walk_pgd_level_debugfs(struct seq_file *m, struct mm_struct *mm,
void ptdump_walk_pgd_level_checkwx(void);
void ptdump_walk_user_pgd_level_checkwx(void);

+/*
+ * Macros to add or remove encryption attribute
+ */
+#ifdef CONFIG_ARCH_HAS_CC_PLATFORM
+pgprot_t pgprot_encrypted(pgprot_t prot);
+pgprot_t pgprot_decrypted(pgprot_t prot);
+#define pgprot_encrypted(prot) pgprot_encrypted(prot)
+#define pgprot_decrypted(prot) pgprot_decrypted(prot)
+#else
+#define pgprot_encrypted(prot) (prot)
+#define pgprot_decrypted(prot) (prot)
+#endif
+
#ifdef CONFIG_DEBUG_WX
#define debug_checkwx() ptdump_walk_pgd_level_checkwx()
#define debug_checkwx_user() ptdump_walk_user_pgd_level_checkwx()
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 4bcaadf21dc6..c6a279e67dff 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -55,6 +55,8 @@ void tdx_safe_halt(void);

bool tdx_early_handle_ve(struct pt_regs *regs);

+phys_addr_t tdx_shared_mask(void);
+
#else

static inline void tdx_early_init(void) { };
@@ -63,6 +65,8 @@ static inline void tdx_safe_halt(void) { };

static inline bool tdx_early_handle_ve(struct pt_regs *regs) { return false; }

+static inline phys_addr_t tdx_shared_mask(void) { return 0; }
+
#endif /* CONFIG_INTEL_TDX_GUEST */

#if defined(CONFIG_KVM_GUEST) && defined(CONFIG_INTEL_TDX_GUEST)
diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c
index dcb31d6a7554..be8722ad4792 100644
--- a/arch/x86/kernel/cc_platform.c
+++ b/arch/x86/kernel/cc_platform.c
@@ -12,6 +12,7 @@
#include <linux/mem_encrypt.h>

#include <asm/mshyperv.h>
+#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/tdx.h>

@@ -90,3 +91,25 @@ bool cc_platform_has(enum cc_attr attr)
return false;
}
EXPORT_SYMBOL_GPL(cc_platform_has);
+
+pgprot_t pgprot_encrypted(pgprot_t prot)
+{
+ if (sme_me_mask)
+ return __pgprot(__sme_set(pgprot_val(prot)));
+ else if (is_tdx_guest())
+ return __pgprot(pgprot_val(prot) & ~tdx_shared_mask());
+
+ return prot;
+}
+EXPORT_SYMBOL_GPL(pgprot_encrypted);
+
+pgprot_t pgprot_decrypted(pgprot_t prot)
+{
+ if (sme_me_mask)
+ return __pgprot(__sme_clr(pgprot_val(prot)));
+ else if (is_tdx_guest())
+ return __pgprot(pgprot_val(prot) | tdx_shared_mask());
+
+ return prot;
+}
+EXPORT_SYMBOL_GPL(pgprot_decrypted);
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index beeaf61934bc..3bf6621eae7d 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -66,6 +66,15 @@ long tdx_kvm_hypercall(unsigned int nr, unsigned long p1, unsigned long p2,
EXPORT_SYMBOL_GPL(tdx_kvm_hypercall);
#endif

+/*
+ * The highest bit of a guest physical address is the "sharing" bit.
+ * Set it for shared pages and clear it for private pages.
+ */
+phys_addr_t tdx_shared_mask(void)
+{
+ return BIT_ULL(td_info.gpa_width - 1);
+}
+
static void tdx_get_info(void)
{
struct tdx_module_output out;
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 026031b3b782..a5d4ec1afca2 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -242,10 +242,15 @@ __ioremap_caller(resource_size_t phys_addr, unsigned long size,
* If the page being mapped is in memory and SEV is active then
* make sure the memory encryption attribute is enabled in the
* resulting mapping.
+ * In TDX guests, memory is marked private by default. If encryption
+ * is not requested (using encrypted), explicitly set decrypt
+ * attribute in all IOREMAPPED memory.
*/
prot = PAGE_KERNEL_IO;
if ((io_desc.flags & IORES_MAP_ENCRYPTED) || encrypted)
prot = pgprot_encrypted(prot);
+ else
+ prot = pgprot_decrypted(prot);

switch (pcm) {
case _PAGE_CACHE_MODE_UC:
--
2.34.1