drivers/virt: pkvm: Hook up mem_encrypt API using pKVM hypercalls

If we detect the presence of pKVM's SHARE and UNSHARE hypercalls, then
register a backend implementation of the mem_encrypt API so that things
like DMA buffers can be shared appropriately with the host.
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240830130150.8568-5-will@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

Documentation/virt/kvm/arm/hypercalls.rst

@@ -66,3 +66,53 @@ Query the memory protection parameters for a pKVM protected virtual machine.
 | Return Values:      | (int64)  | R0 | ``INVALID_PARAMETER (-3)`` on error, else   |
 |                     |          |    | memory protection granule in bytes          |
 +---------------------+----------+----+---------------------------------------------+
+
+``ARM_SMCCC_KVM_FUNC_MEM_SHARE``
+--------------------------------
+
+Share a region of memory with the KVM host, granting it read, write and execute
+permissions. The size of the region is equal to the memory protection granule
+advertised by ``ARM_SMCCC_KVM_FUNC_HYP_MEMINFO``.
+
++---------------------+-------------------------------------------------------------+
+| Presence:           | Optional; pKVM protected guests only.                       |
++---------------------+-------------------------------------------------------------+
+| Calling convention: | HVC64                                                       |
++---------------------+----------+--------------------------------------------------+
+| Function ID:        | (uint32) | 0xC6000003                                       |
++---------------------+----------+----+---------------------------------------------+
+| Arguments:          | (uint64) | R1 | Base IPA of memory region to share          |
+|                     +----------+----+---------------------------------------------+
+|                     | (uint64) | R2 | Reserved / Must be zero                     |
+|                     +----------+----+---------------------------------------------+
+|                     | (uint64) | R3 | Reserved / Must be zero                     |
++---------------------+----------+----+---------------------------------------------+
+| Return Values:      | (int64)  | R0 | ``SUCCESS (0)``                             |
+|                     |          |    +---------------------------------------------+
+|                     |          |    | ``INVALID_PARAMETER (-3)``                  |
++---------------------+----------+----+---------------------------------------------+
+
+``ARM_SMCCC_KVM_FUNC_MEM_UNSHARE``
+----------------------------------
+
+Revoke access permission from the KVM host to a memory region previously shared
+with ``ARM_SMCCC_KVM_FUNC_MEM_SHARE``. The size of the region is equal to the
+memory protection granule advertised by ``ARM_SMCCC_KVM_FUNC_HYP_MEMINFO``.
+
++---------------------+-------------------------------------------------------------+
+| Presence:           | Optional; pKVM protected guests only.                       |
++---------------------+-------------------------------------------------------------+
+| Calling convention: | HVC64                                                       |
++---------------------+----------+--------------------------------------------------+
+| Function ID:        | (uint32) | 0xC6000004                                       |
++---------------------+----------+----+---------------------------------------------+
+| Arguments:          | (uint64) | R1 | Base IPA of memory region to unshare        |
+|                     +----------+----+---------------------------------------------+
+|                     | (uint64) | R2 | Reserved / Must be zero                     |
+|                     +----------+----+---------------------------------------------+
+|                     | (uint64) | R3 | Reserved / Must be zero                     |
++---------------------+----------+----+---------------------------------------------+
+| Return Values:      | (int64)  | R0 | ``SUCCESS (0)``                             |
+|                     |          |    +---------------------------------------------+
+|                     |          |    | ``INVALID_PARAMETER (-3)``                  |
++---------------------+----------+----+---------------------------------------------+

drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c

@@ -9,18 +9,72 @@
 
 #include <linux/arm-smccc.h>
 #include <linux/array_size.h>
+#include <linux/mem_encrypt.h>
 #include <linux/mm.h>
 
 #include <asm/hypervisor.h>
 
 static size_t pkvm_granule;
 
+static int arm_smccc_do_one_page(u32 func_id, phys_addr_t phys)
+{
+	phys_addr_t end = phys + PAGE_SIZE;
+
+	while (phys < end) {
+		struct arm_smccc_res res;
+
+		arm_smccc_1_1_invoke(func_id, phys, 0, 0, &res);
+		if (res.a0 != SMCCC_RET_SUCCESS)
+			return -EPERM;
+
+		phys += pkvm_granule;
+	}
+
+	return 0;
+}
+
+static int __set_memory_range(u32 func_id, unsigned long start, int numpages)
+{
+	void *addr = (void *)start, *end = addr + numpages * PAGE_SIZE;
+
+	while (addr < end) {
+		int err;
+
+		err = arm_smccc_do_one_page(func_id, virt_to_phys(addr));
+		if (err)
+			return err;
+
+		addr += PAGE_SIZE;
+	}
+
+	return 0;
+}
+
+static int pkvm_set_memory_encrypted(unsigned long addr, int numpages)
+{
+	return __set_memory_range(ARM_SMCCC_VENDOR_HYP_KVM_MEM_UNSHARE_FUNC_ID,
+				  addr, numpages);
+}
+
+static int pkvm_set_memory_decrypted(unsigned long addr, int numpages)
+{
+	return __set_memory_range(ARM_SMCCC_VENDOR_HYP_KVM_MEM_SHARE_FUNC_ID,
+				  addr, numpages);
+}
+
+static const struct arm64_mem_crypt_ops pkvm_crypt_ops = {
+	.encrypt	= pkvm_set_memory_encrypted,
+	.decrypt	= pkvm_set_memory_decrypted,
+};
+
 void pkvm_init_hyp_services(void)
 {
 	int i;
 	struct arm_smccc_res res;
 	const u32 funcs[] = {
 		ARM_SMCCC_KVM_FUNC_HYP_MEMINFO,
+		ARM_SMCCC_KVM_FUNC_MEM_SHARE,
+		ARM_SMCCC_KVM_FUNC_MEM_UNSHARE,
 	};
 
 	for (i = 0; i < ARRAY_SIZE(funcs); ++i) {
@@ -34,4 +88,5 @@ void pkvm_init_hyp_services(void)
 		return;
 
 	pkvm_granule = res.a0;
+	arm64_mem_crypt_ops_register(&pkvm_crypt_ops);
 }

include/linux/arm-smccc.h

@@ -116,6 +116,8 @@
 #define ARM_SMCCC_KVM_FUNC_FEATURES		0
 #define ARM_SMCCC_KVM_FUNC_PTP			1
 #define ARM_SMCCC_KVM_FUNC_HYP_MEMINFO		2
+#define ARM_SMCCC_KVM_FUNC_MEM_SHARE		3
+#define ARM_SMCCC_KVM_FUNC_MEM_UNSHARE		4
 #define ARM_SMCCC_KVM_FUNC_FEATURES_2		127
 #define ARM_SMCCC_KVM_NUM_FUNCS			128
 
@@ -144,6 +146,18 @@
 			   ARM_SMCCC_OWNER_VENDOR_HYP,			\
 			   ARM_SMCCC_KVM_FUNC_HYP_MEMINFO)
 
+#define ARM_SMCCC_VENDOR_HYP_KVM_MEM_SHARE_FUNC_ID			\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_64,				\
+			   ARM_SMCCC_OWNER_VENDOR_HYP,			\
+			   ARM_SMCCC_KVM_FUNC_MEM_SHARE)
+
+#define ARM_SMCCC_VENDOR_HYP_KVM_MEM_UNSHARE_FUNC_ID			\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_64,				\
+			   ARM_SMCCC_OWNER_VENDOR_HYP,			\
+			   ARM_SMCCC_KVM_FUNC_MEM_UNSHARE)
+
 /* ptp_kvm counter type ID */
 #define KVM_PTP_VIRT_COUNTER			0
 #define KVM_PTP_PHYS_COUNTER			1