[PATCH 4/7] x86/ioremap, resource: Introduce IORES_DESC_ENCRYPTED for encrypted PCI MMIO

[Dan Williams <dan.j.williams@intel.com>]

PCIe Trusted Execution Environment Device Interface Security Protocol
(TDISP) arranges for a PCI device to support encrypted MMIO. In support of
that capability, ioremap() needs a mechanism to detect when a PCI device
has been dynamically transitioned into this secure state and enforce
encrypted MMIO mappings.

Teach ioremap() about a new IORES_DESC_ENCRYPTED type that supplements the
existing PCI Memory Space (MMIO) BAR resources. The proposal is that a
resource, "PCI MMIO Encrypted", with this description type is injected by
the PCI/TSM core for each PCI device BAR that is to be protected.

Unlike the existing encryption determination which is "implied with a silent
fallback to an unencrypted mapping", this indication is "explicit with an
expectation that the request fails instead of fallback". IORES_MUST_ENCRYPT
is added to manage this expectation.

Given that "PCI MMIO Encrypted" is an additional resource in the tree, the
IORESOURCE_BUSY flag will only be set on a descendant/child of that
resource. Adjust the resource tree walk to use walk_iomem_res_desc() and
check all intersecting resources for the IORES_MUST_ENCRYPT determination.

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 arch/x86/mm/ioremap.c  | 32 +++++++++++++++++++++-----------
 include/linux/ioport.h |  2 ++
 2 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 12c8180ca1ba..78b677dadfdc 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -93,18 +93,24 @@ static unsigned int __ioremap_check_ram(struct resource *res)
  */
 static unsigned int __ioremap_check_encrypted(struct resource *res)
 {
+	u32 flags = 0;
+
+	if (res->desc == IORES_DESC_ENCRYPTED)
+		flags |= IORES_MUST_ENCRYPT;
+
 	if (!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
-		return 0;
+		return flags;
 
 	switch (res->desc) {
 	case IORES_DESC_NONE:
 	case IORES_DESC_RESERVED:
 		break;
+	case IORES_DESC_ENCRYPTED:
 	default:
-		return IORES_MAP_ENCRYPTED;
+		flags |= IORES_MAP_ENCRYPTED;
 	}
 
-	return 0;
+	return flags;
 }
 
 /*
@@ -134,14 +140,10 @@ static int __ioremap_collect_map_flags(struct resource *res, void *arg)
 {
 	struct ioremap_desc *desc = arg;
 
-	if (!(desc->flags & IORES_MAP_SYSTEM_RAM))
-		desc->flags |= __ioremap_check_ram(res);
-
-	if (!(desc->flags & IORES_MAP_ENCRYPTED))
-		desc->flags |= __ioremap_check_encrypted(res);
+	desc->flags |= __ioremap_check_ram(res);
+	desc->flags |= __ioremap_check_encrypted(res);
 
-	return ((desc->flags & (IORES_MAP_SYSTEM_RAM | IORES_MAP_ENCRYPTED)) ==
-			       (IORES_MAP_SYSTEM_RAM | IORES_MAP_ENCRYPTED));
+	return 0;
 }
 
 /*
@@ -161,7 +163,8 @@ static void __ioremap_check_mem(resource_size_t addr, unsigned long size,
 	end = start + size - 1;
 	memset(desc, 0, sizeof(struct ioremap_desc));
 
-	walk_mem_res(start, end, desc, __ioremap_collect_map_flags);
+	walk_iomem_res_desc(IORES_DESC_NONE, IORESOURCE_MEM, start, end, desc,
+			    __ioremap_collect_map_flags);
 
 	__ioremap_check_other(addr, desc);
 }
@@ -209,6 +212,13 @@ __ioremap_caller(resource_size_t phys_addr, unsigned long size,
 
 	__ioremap_check_mem(phys_addr, size, &io_desc);
 
+	if ((io_desc.flags & IORES_MUST_ENCRYPT) &&
+	    !(io_desc.flags & IORES_MAP_ENCRYPTED)) {
+		pr_err("ioremap: encrypted mapping unavailable for %pa - %pa\n",
+		       &phys_addr, &last_addr);
+		return NULL;
+	}
+
 	/*
 	 * Don't allow anybody to remap normal RAM that we're using..
 	 */
diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index e8b2d6aa4013..b46e42bcafe3 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -143,6 +143,7 @@ enum {
 	IORES_DESC_RESERVED			= 7,
 	IORES_DESC_SOFT_RESERVED		= 8,
 	IORES_DESC_CXL				= 9,
+	IORES_DESC_ENCRYPTED			= 10,
 };
 
 /*
@@ -151,6 +152,7 @@ enum {
 enum {
 	IORES_MAP_SYSTEM_RAM		= BIT(0),
 	IORES_MAP_ENCRYPTED		= BIT(1),
+	IORES_MUST_ENCRYPT		= BIT(2), /* disable transparent fallback */
 };
 
 /* helpers to define resources */
-- 
2.50.1