drivers/virt: pkvm: Intercept ioremap using pKVM MMIO_GUARD hypercall

Hook up pKVM's MMIO_GUARD hypercall so that ioremap() and friends will
register the target physical address as MMIO with the hypervisor,
allowing guest exits to that page to be emulated by the host with full
syndrome information.

Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240830130150.8568-7-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c b/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c
index 8256cf68fd76..56a3859dda8a 100644
--- a/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c
+++ b/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c
@@ -9,8 +9,10 @@
 
 #include <linux/arm-smccc.h>
 #include <linux/array_size.h>
+#include <linux/io.h>
 #include <linux/mem_encrypt.h>
 #include <linux/mm.h>
+#include <linux/pgtable.h>
 
 #include <asm/hypervisor.h>
 
@@ -67,6 +69,36 @@ static const struct arm64_mem_crypt_ops pkvm_crypt_ops = {
 	.decrypt	= pkvm_set_memory_decrypted,
 };
 
+static int mmio_guard_ioremap_hook(phys_addr_t phys, size_t size,
+				   pgprot_t *prot)
+{
+	phys_addr_t end;
+	pteval_t protval = pgprot_val(*prot);
+
+	/*
+	 * We only expect MMIO emulation for regions mapped with device
+	 * attributes.
+	 */
+	if (protval != PROT_DEVICE_nGnRE && protval != PROT_DEVICE_nGnRnE)
+		return 0;
+
+	phys = PAGE_ALIGN_DOWN(phys);
+	end = phys + PAGE_ALIGN(size);
+
+	while (phys < end) {
+		const int func_id = ARM_SMCCC_VENDOR_HYP_KVM_MMIO_GUARD_FUNC_ID;
+		int err;
+
+		err = arm_smccc_do_one_page(func_id, phys);
+		if (err)
+			return err;
+
+		phys += PAGE_SIZE;
+	}
+
+	return 0;
+}
+
 void pkvm_init_hyp_services(void)
 {
 	int i;
@@ -89,4 +121,7 @@ void pkvm_init_hyp_services(void)
 
 	pkvm_granule = res.a0;
 	arm64_mem_crypt_ops_register(&pkvm_crypt_ops);
+
+	if (kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_MMIO_GUARD))
+		arm64_ioremap_prot_hook_register(&mmio_guard_ioremap_hook);
 }