KVM: arm64: Introduce an early Hyp page allocator

With nVHE, the host currently creates all stage 1 hypervisor mappings at
EL1 during boot, installs them at EL2, and extends them as required
(e.g. when creating a new VM). But in a world where the host is no
longer trusted, it cannot have full control over the code mapped in the
hypervisor.

In preparation for enabling the hypervisor to create its own stage 1
mappings during boot, introduce an early page allocator, with minimal
functionality. This allocator is designed to be used only during early
bootstrap of the hyp code when memory protection is enabled, which will
then switch to using a full-fledged page allocator after init.
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210319100146.1149909-11-qperret@google.com

arch/arm64/kvm/hyp/include/nvhe/early_alloc.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __KVM_HYP_EARLY_ALLOC_H
+#define __KVM_HYP_EARLY_ALLOC_H
+
+#include <asm/kvm_pgtable.h>
+
+void hyp_early_alloc_init(void *virt, unsigned long size);
+unsigned long hyp_early_alloc_nr_used_pages(void);
+void *hyp_early_alloc_page(void *arg);
+void *hyp_early_alloc_contig(unsigned int nr_pages);
+
+extern struct kvm_pgtable_mm_ops hyp_early_alloc_mm_ops;
+
+#endif /* __KVM_HYP_EARLY_ALLOC_H */

arch/arm64/kvm/hyp/include/nvhe/memory.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __KVM_HYP_MEMORY_H
+#define __KVM_HYP_MEMORY_H
+
+#include <asm/page.h>
+
+#include <linux/types.h>
+
+extern s64 hyp_physvirt_offset;
+
+#define __hyp_pa(virt)	((phys_addr_t)(virt) + hyp_physvirt_offset)
+#define __hyp_va(phys)	((void *)((phys_addr_t)(phys) - hyp_physvirt_offset))
+
+static inline void *hyp_phys_to_virt(phys_addr_t phys)
+{
+	return __hyp_va(phys);
+}
+
+static inline phys_addr_t hyp_virt_to_phys(void *addr)
+{
+	return __hyp_pa(addr);
+}
+
+#endif /* __KVM_HYP_MEMORY_H */

arch/arm64/kvm/hyp/nvhe/Makefile

@@ -13,7 +13,7 @@ lib-objs := clear_page.o copy_page.o memcpy.o memset.o
 lib-objs := $(addprefix ../../../lib/, $(lib-objs))
 
 obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o \
-	 hyp-main.o hyp-smp.o psci-relay.o
+	 hyp-main.o hyp-smp.o psci-relay.o early_alloc.o
 obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
 	 ../fpsimd.o ../hyp-entry.o ../exception.o
 obj-y += $(lib-objs)

arch/arm64/kvm/hyp/nvhe/early_alloc.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 Google LLC
+ * Author: Quentin Perret <qperret@google.com>
+ */
+
+#include <asm/kvm_pgtable.h>
+
+#include <nvhe/early_alloc.h>
+#include <nvhe/memory.h>
+
+struct kvm_pgtable_mm_ops hyp_early_alloc_mm_ops;
+s64 __ro_after_init hyp_physvirt_offset;
+
+static unsigned long base;
+static unsigned long end;
+static unsigned long cur;
+
+unsigned long hyp_early_alloc_nr_used_pages(void)
+{
+	return (cur - base) >> PAGE_SHIFT;
+}
+
+void *hyp_early_alloc_contig(unsigned int nr_pages)
+{
+	unsigned long size = (nr_pages << PAGE_SHIFT);
+	void *ret = (void *)cur;
+
+	if (!nr_pages)
+		return NULL;
+
+	if (end - cur < size)
+		return NULL;
+
+	cur += size;
+	memset(ret, 0, size);
+
+	return ret;
+}
+
+void *hyp_early_alloc_page(void *arg)
+{
+	return hyp_early_alloc_contig(1);
+}
+
+void hyp_early_alloc_init(void *virt, unsigned long size)
+{
+	base = cur = (unsigned long)virt;
+	end = base + size;
+
+	hyp_early_alloc_mm_ops.zalloc_page = hyp_early_alloc_page;
+	hyp_early_alloc_mm_ops.phys_to_virt = hyp_phys_to_virt;
+	hyp_early_alloc_mm_ops.virt_to_phys = hyp_virt_to_phys;
+}

arch/arm64/kvm/hyp/nvhe/psci-relay.c

@@ -11,6 +11,7 @@
 #include <linux/kvm_host.h>
 #include <uapi/linux/psci.h>
 
+#include <nvhe/memory.h>
 #include <nvhe/trap_handler.h>
 
 void kvm_hyp_cpu_entry(unsigned long r0);
@@ -20,9 +21,6 @@ void __noreturn __host_enter(struct kvm_cpu_context *host_ctxt);
 
 /* Config options set by the host. */
 struct kvm_host_psci_config __ro_after_init kvm_host_psci_config;
-s64 __ro_after_init hyp_physvirt_offset;
-
-#define __hyp_pa(x) ((phys_addr_t)((x)) + hyp_physvirt_offset)
 
 #define INVALID_CPU_ID	UINT_MAX