ANDROID: Define mem_relinquish interface for releasing memory to a hypervisor.

On PKVM/ARM64 this uses the ARM SMCCC relinquish hypercall when available.

Bug: 240239989
Change-Id: Ifa85b641a48f348a2364cf8c6b06b6417f1eeedb
Signed-off-by: Keir Fraser <keirf@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>

arch/Kconfig

@@ -1316,6 +1316,9 @@ config RELR
 config ARCH_HAS_MEM_ENCRYPT
 	bool
 
+config ARCH_HAS_MEM_RELINQUISH
+	bool
+
 config ARCH_HAS_CC_PLATFORM
 	bool
 

arch/arm64/Kconfig

@@ -33,6 +33,7 @@ config ARM64
 	select ARCH_HAS_KEEPINITRD
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_MEM_ENCRYPT
+	select ARCH_HAS_MEM_RELINQUISH
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	select ARCH_HAS_PTE_DEVMAP
 	select ARCH_HAS_PTE_SPECIAL

arch/arm64/include/asm/hypervisor.h

@@ -10,4 +10,10 @@ void kvm_arm_init_hyp_services(void);
 void kvm_init_memshare_services(void);
 void kvm_init_ioremap_services(void);
 
+#ifdef CONFIG_MEMORY_BALLOON
+void kvm_init_memrelinquish_services(void);
+#else
+static inline void kvm_init_memrelinquish_services(void) {}
+#endif
+
 #endif

arch/arm64/include/asm/mem_relinquish.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2022 Google LLC
+ * Author: Keir Fraser <keirf@google.com>
+ */
+
+#ifndef __ASM_MEM_RELINQUISH_H
+#define __ASM_MEM_RELINQUISH_H
+
+void page_relinquish(struct page *page);
+
+#endif	/* __ASM_MEM_RELINQUISH_H */

arch/arm64/kernel/setup.c

@@ -445,4 +445,5 @@ void kvm_arm_init_hyp_services(void)
 {
 	kvm_init_ioremap_services();
 	kvm_init_memshare_services();
+	kvm_init_memrelinquish_services();
 }

arch/arm64/mm/Makefile

@@ -3,6 +3,7 @@ obj-y				:= dma-mapping.o extable.o fault.o init.o \
 				   cache.o copypage.o flush.o \
 				   ioremap.o mem_encrypt.o mmap.o pgd.o mmu.o \
 				   context.o proc.o pageattr.o
+obj-$(CONFIG_MEMORY_BALLOON)	+= mem_relinquish.o
 obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o
 obj-$(CONFIG_PTDUMP_CORE)	+= ptdump.o
 obj-$(CONFIG_PTDUMP_DEBUGFS)	+= ptdump_debugfs.o

arch/arm64/mm/mem_relinquish.c

@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2022 Google LLC
+ * Author: Keir Fraser <keirf@google.com>
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/memory.h>
+#include <linux/mm.h>
+#include <linux/types.h>
+
+#include <asm/hypervisor.h>
+
+static unsigned long memshare_granule_sz;
+
+void kvm_init_memrelinquish_services(void)
+{
+	int i;
+	struct arm_smccc_res res;
+	const u32 funcs[] = {
+		ARM_SMCCC_KVM_FUNC_HYP_MEMINFO,
+		ARM_SMCCC_KVM_FUNC_MEM_RELINQUISH,
+	};
+
+	for (i = 0; i < ARRAY_SIZE(funcs); ++i) {
+		if (!kvm_arm_hyp_service_available(funcs[i]))
+			return;
+	}
+
+	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_HYP_MEMINFO_FUNC_ID,
+			     0, 0, 0, &res);
+	if (res.a0 > PAGE_SIZE) /* Includes error codes */
+		return;
+
+	memshare_granule_sz = res.a0;
+}
+
+void page_relinquish(struct page *page)
+{
+	phys_addr_t phys, end;
+	u32 func_id = ARM_SMCCC_VENDOR_HYP_KVM_MEM_RELINQUISH_FUNC_ID;
+
+	if (!memshare_granule_sz)
+		return;
+
+	phys = page_to_phys(page);
+	end = phys + PAGE_SIZE;
+
+	while (phys < end) {
+		struct arm_smccc_res res;
+
+		arm_smccc_1_1_invoke(func_id, phys, 0, 0, &res);
+		BUG_ON(res.a0 != SMCCC_RET_SUCCESS);
+
+		phys += memshare_granule_sz;
+	}
+}
+EXPORT_SYMBOL_GPL(page_relinquish);

include/linux/mem_relinquish.h

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2022 Google LLC
+ * Author: Keir Fraser <keirf@google.com>
+ */
+
+#ifndef __MEM_RELINQUISH_H__
+#define __MEM_RELINQUISH_H__
+
+#ifdef CONFIG_ARCH_HAS_MEM_RELINQUISH
+
+#include <asm/mem_relinquish.h>
+
+#else	/* !CONFIG_ARCH_HAS_MEM_RELINQUISH */
+
+static inline void page_relinquish(struct page *page) { }
+
+#endif	/* CONFIG_ARCH_HAS_MEM_RELINQUISH */
+
+#endif	/* __MEM_RELINQUISH_H__ */