[PATCH v3 02/13] KVM: arm64: Take host-registered MMIO regions at pKVM finalisation

[Fuad Tabba <fuad.tabba@linux.dev>]

From: Sebastian Ene <sebastianene@google.com>

To mediate a device, the protected KVM hypervisor has to own its
registers, so that a host access to them takes a stage-2 abort rather
than reaching the device.

Let the host register MMIO regions before the hypervisor initialises,
and have __pkvm_init_finalise() donate each one and record where it's
mapped in the hypervisor's private range. The donation runs before
pkvm_check_host_ownership(), which then covers those mappings too. A
failed donation fails the hypervisor's initialisation before the host
stage 2 is installed, so nothing is given back.

Nothing registers a region yet.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
Co-developed-by: Fuad Tabba <fuad.tabba@linux.dev>
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---

Notes:
    Changes since v2 (v2 patches 02 and 03, merged):
    - The trap handling moved to patch 9, which calls the ITS emulation
      directly (was a per-region callback)
    - Each region records its hypervisor VA
    - A failed donation is no longer unwound

 arch/arm64/include/asm/kvm_pkvm.h     | 12 ++++++++++++
 arch/arm64/kvm/hyp/nvhe/mem_protect.c |  3 +++
 arch/arm64/kvm/hyp/nvhe/setup.c       | 22 ++++++++++++++++++++++
 3 files changed, 37 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
index fd042d2b54624..4695c35b31e1a 100644
--- a/arch/arm64/include/asm/kvm_pkvm.h
+++ b/arch/arm64/include/asm/kvm_pkvm.h
@@ -17,6 +17,18 @@
 
 #define HYP_MEMBLOCK_REGIONS 128
 
+/* MMIO regions the host registers for the hypervisor to take at finalisation. */
+#define PKVM_PROTECTED_REGS_NUM	8
+
+struct pkvm_protected_reg {
+	u64			pfn;
+	u64			nr_pages;
+	void __iomem		*hyp_va;
+};
+
+extern struct pkvm_protected_reg kvm_nvhe_sym(pkvm_protected_regs)[];
+extern unsigned int kvm_nvhe_sym(num_protected_reg);
+
 int pkvm_init_host_vm(struct kvm *kvm);
 int pkvm_create_hyp_vm(struct kvm *kvm);
 bool pkvm_hyp_vm_is_created(struct kvm *kvm);
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index a6dacaca77610..8d45f45d30e6a 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -28,6 +28,9 @@ struct host_mmu host_mmu;
 
 static struct hyp_pool host_s2_pool;
 
+unsigned int num_protected_reg;
+struct pkvm_protected_reg pkvm_protected_regs[PKVM_PROTECTED_REGS_NUM];
+
 static DEFINE_PER_CPU(struct pkvm_hyp_vm *, __current_vm);
 #define current_vm (*this_cpu_ptr(&__current_vm))
 
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 7bbc26b28faa5..18f348d1331a8 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -295,6 +295,24 @@ static int fix_hyp_pgtable_refcnt(void)
 				&walker);
 }
 
+static int donate_protected_mmio_regions(void)
+{
+	struct pkvm_protected_reg *region;
+	unsigned long haddr;
+	int ret, i;
+
+	for (i = 0; i < num_protected_reg; i++) {
+		region = &pkvm_protected_regs[i];
+		ret = __pkvm_host_donate_hyp_mmio(region->pfn, region->nr_pages, &haddr);
+		if (ret)
+			return ret;
+
+		region->hyp_va = (void __iomem *)haddr;
+	}
+
+	return 0;
+}
+
 void __noreturn __pkvm_init_finalise(void)
 {
 	struct kvm_cpu_context *host_ctxt = host_data_ptr(host_ctxt);
@@ -335,6 +353,10 @@ void __noreturn __pkvm_init_finalise(void)
 	if (ret)
 		goto out;
 
+	ret = donate_protected_mmio_regions();
+	if (ret)
+		goto out;
+
 	ret = pkvm_check_host_ownership();
 	if (ret)
 		goto out;
-- 
2.47.3