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Subject[PATCH 19/26] x86/tdx: Make pages shared in ioremap()
Date
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. Introduce CC_ATTR_GUEST_TDX
to add TDX-specific changes to the AMD SEV/SME memory encryption 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/Kconfig | 2 +-
arch/x86/include/asm/pgtable.h | 19 +++++++++++++------
arch/x86/include/asm/tdx.h | 3 +++
arch/x86/kernel/cc_platform.c | 1 +
arch/x86/kernel/tdx.c | 9 +++++++++
arch/x86/mm/ioremap.c | 5 +++++
arch/x86/mm/mem_encrypt.c | 27 +++++++++++++++++++++++++++
include/linux/cc_platform.h | 9 +++++++++
8 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index fe0382f20445..f5df53b6c80d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -879,7 +879,7 @@ config INTEL_TDX_GUEST
depends on X86_X2APIC
select ARCH_HAS_CC_PLATFORM
select X86_MCE
- select DYNAMIC_PHYSICAL_MASK
+ select X86_MEM_ENCRYPT
help
Support running as a guest under Intel TDX. Without this support,
the guest kernel can not boot or run under TDX.
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 448cd01eb3ec..019cb2f97c20 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 <asm/x86_init.h>
#include <asm/pkru.h>
@@ -36,6 +30,19 @@ 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_X86_MEM_ENCRYPT
+pgprot_t pgprot_cc_encrypted(pgprot_t prot);
+pgprot_t pgprot_cc_decrypted(pgprot_t prot);
+#define pgprot_encrypted(prot) pgprot_cc_encrypted(prot)
+#define pgprot_decrypted(prot) pgprot_cc_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 d2ffc9a6ba53..286adda40fb7 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -76,6 +76,8 @@ void tdx_guest_idle(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) { };
@@ -83,6 +85,7 @@ static inline bool is_tdx_guest(void) { return false; }
static inline void tdx_guest_idle(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 */

diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c
index 2ed8652ab042..a0fc329edc35 100644
--- a/arch/x86/kernel/cc_platform.c
+++ b/arch/x86/kernel/cc_platform.c
@@ -19,6 +19,7 @@ static bool intel_cc_platform_has(enum cc_attr attr)
switch (attr) {
case CC_ATTR_GUEST_UNROLL_STRING_IO:
case CC_ATTR_HOTPLUG_DISABLED:
+ case CC_ATTR_GUEST_TDX:
return true;
default:
return false;
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index cbfacc2af8bb..d4aae2f139a8 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -52,6 +52,15 @@ static inline u64 _tdx_hypercall(u64 fn, u64 r12, u64 r13, u64 r14,
return out->r10;
}

+/*
+ * 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:
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 50d209939c66..8b9de7e478c6 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -14,6 +14,33 @@
#include <linux/mem_encrypt.h>
#include <linux/virtio_config.h>

+#include <asm/tdx.h>
+
+/*
+ * Set or unset encryption attribute in vendor agnostic way.
+ */
+pgprot_t pgprot_cc_encrypted(pgprot_t prot)
+{
+ if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
+ return __pgprot(__sme_set(pgprot_val(prot)));
+ else if (cc_platform_has(CC_ATTR_GUEST_TDX))
+ return __pgprot(pgprot_val(prot) & ~tdx_shared_mask());
+
+ return prot;
+}
+EXPORT_SYMBOL_GPL(pgprot_cc_encrypted);
+
+pgprot_t pgprot_cc_decrypted(pgprot_t prot)
+{
+ if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
+ return __pgprot(__sme_clr(pgprot_val(prot)));
+ else if (cc_platform_has(CC_ATTR_GUEST_TDX))
+ return __pgprot(pgprot_val(prot) | tdx_shared_mask());
+
+ return prot;
+}
+EXPORT_SYMBOL_GPL(pgprot_cc_decrypted);
+
/* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
bool force_dma_unencrypted(struct device *dev)
{
diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
index 63b15108bc85..5fed077cc5f4 100644
--- a/include/linux/cc_platform.h
+++ b/include/linux/cc_platform.h
@@ -82,6 +82,15 @@ enum cc_attr {
* Examples include TDX Guest.
*/
CC_ATTR_HOTPLUG_DISABLED,
+
+ /**
+ * @CC_ATTR_GUEST_TDX: Trust Domain Extension Support
+ *
+ * The platform/OS is running as a TDX guest/virtual machine.
+ *
+ * Examples include Intel TDX.
+ */
+ CC_ATTR_GUEST_TDX = 0x100,
};

#ifdef CONFIG_ARCH_HAS_CC_PLATFORM
--
2.32.0
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