LKL MMU support

.github/workflows/ci.yml

@@ -22,6 +22,11 @@ jobs:
             runs_on: ubuntu-22.04
             shell: bash
             build_options: "kasan=yes kasan_test=yes"
+          - displayTargetName: mmu_kasan
+            os: unix
+            runs_on: ubuntu-22.04
+            shell: bash
+            build_options: "MMU=1 MMU_KUNIT=1 kasan=yes"
           - displayTargetName: windows-2019
             os: windows
             runs_on: windows-2019

arch/lkl/Kconfig

@@ -1,6 +1,6 @@
 config LKL
        def_bool y
-       depends on !SMP && !MMU && !COREDUMP && !SECCOMP && !UPROBES && !COMPAT && !USER_RETURN_NOTIFIER
+       depends on !SMP && !COREDUMP && !SECCOMP && !UPROBES && !COMPAT && !USER_RETURN_NOTIFIER
        select ARCH_THREAD_STACK_ALLOCATOR
        select RWSEM_GENERIC_SPINLOCK
        select GENERIC_ATOMIC64
@@ -77,6 +77,43 @@ config 64BIT
        bool "64bit kernel"
        default n
 
+config MMU
+       bool "LKL MMU implementation"
+       depends on 64BIT
+       default n
+
+if MMU
+config PGTABLE_LEVELS
+       int
+       default 3
+
+config LKL_MEMORY_START
+       hex
+       default 0x50000000
+       help
+         Base address of kernel virtual address space for LKL. No particular
+         reason for picking this specific value. It is assumed that the host
+         mmap is able to map requested amount of memory at this address.
+         STACK_TOP and VMALLOC_START values depend on it.
+
+
+config LKL_TASK_UNMAPPED_BASE
+       hex
+       default 0x100000
+       help
+         Starting virtual address for LKL user-space mmap. It is assumed that
+         the host mmap is able to map requested amount of memory starting from
+         this address.
+
+config LKL_MMU_KUNIT_TEST
+       bool "Kunit tests for LKL MMU"
+       default n
+       depends on KUNIT
+       help
+         Kunit tests to test correctness of MMU-related kernel interfaces (such
+         as vmalloc, for example) which are difficult to test in user-space.
+endif
+
 config COREDUMP
        def_bool n
 

arch/lkl/include/asm/Kbuild

@@ -75,3 +75,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += kprobes.h
 generic-y += uaccess.h
+generic-y += mman.h

arch/lkl/include/asm/elf.h

@@ -9,6 +9,13 @@
 #define ELF_CLASS ELFCLASS32
 #endif
 
+#ifdef CONFIG_MMU
+#define ELF_EXEC_PAGESIZE 4096
+#define ELF_PLATFORM "i586"
+#define ELF_HWCAP 0L
+#define ELF_ET_DYN_BASE (TASK_SIZE)
+#endif // CONFIG_MMU
+
 #define elf_gregset_t long
 #define elf_fpregset_t double
 #endif

arch/lkl/include/asm/io.h

@@ -98,6 +98,14 @@ static inline void __iomem *ioremap(phys_addr_t offset, size_t size)
 	return (void __iomem *)lkl_ops->ioremap(offset, size);
 }
 
+#ifdef CONFIG_MMU
+static inline void __iounmap(void __iomem *addr)
+{
+	// No-op according to ioremap implementation.
+}
+#define iounmap __iounmap
+#endif
+
 #include <asm-generic/io.h>
 
 #endif /* _ASM_LKL_IO_H */

arch/lkl/include/asm/mmu_context.h

@@ -2,6 +2,18 @@
 #ifndef _ASM_LKL_MMU_CONTEXT_H
 #define _ASM_LKL_MMU_CONTEXT_H
 
+#ifdef CONFIG_MMU
+static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
+		      struct task_struct *tsk) {
+	// No-op for LKL as it doesn't support multiple user-mode address spaces.
+}
+
+/*  Generic hooks for arch_dup_mmap and arch_exit_mmap  */
+#include <asm-generic/mm_hooks.h>
+#include <asm-generic/mmu_context.h>
+
+#else
 #include <asm-generic/nommu_context.h>
+#endif
 
 #endif /* _ASM_LKL_MMU_CONTEXT_H */

arch/lkl/include/asm/page-mmu.h

@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_LKL_PAGE_MMU_H
+#define _ASM_LKL_PAGE_MMU_H
+
+#include <linux/const.h>
+
+/* PAGE_SHIFT determines the page size */
+#define PAGE_SHIFT	12
+#define PAGE_SIZE	(_AC(1, UL) << PAGE_SHIFT)
+#define PAGE_MASK	(~(PAGE_SIZE-1))
+#define PFN_PTE_SHIFT PAGE_SHIFT
+
+#ifndef __ASSEMBLY__
+
+struct page;
+#define clear_page(page)	memset((void *)(page), 0, PAGE_SIZE)
+#define copy_page(to, from)	memcpy((void *)(to), (void *)(from), PAGE_SIZE)
+#define clear_user_page(page, vaddr, pg)	clear_page(page)
+#define copy_user_page(to, from, vaddr, pg)	copy_page(to, from)
+
+typedef struct {unsigned long pte; } pte_t;
+typedef struct {unsigned long pmd; } pmd_t;
+typedef struct {unsigned long pgd; } pgd_t;
+typedef struct {unsigned long pgprot; } pgprot_t;
+typedef struct page *pgtable_t;
+
+#define pte_val(p) ((p).pte)
+#define pgd_val(x)	((x).pgd)
+#define pgprot_val(x)	((x).pgprot)
+
+#define pmd_val(x)	((x).pmd)
+#define __pmd(x) ((pmd_t) { (x) })
+
+#define __pte(x)	((pte_t) { (x) })
+#define __pgd(x)	((pgd_t) { (x) })
+#define __pgprot(x)	((pgprot_t) { (x) })
+
+#define pte_get_bits(p, bits) ((p).pte & (bits))
+#define pte_set_bits(p, bits) ((p).pte |= (bits))
+#define pte_clear_bits(p, bits) ((p).pte &= ~(bits))
+#define pte_copy(to, from) ({ (to).pte = (from).pte; })
+#define pte_is_zero(p) (!((p).pte & ~_PAGE_NEWPAGE))
+#define pte_set_val(p, phys, prot) ({ (p).pte = (phys) | pgprot_val(prot); })
+
+extern unsigned long memory_start;
+extern unsigned long memory_end;
+
+#define PAGE_OFFSET		(memory_start)
+// Define ARCH_PFN_OFFSET so that kernel virtual addresses are the same as
+// the corresponding physical addresses (i.e. 1-to-1 mapping).
+#define ARCH_PFN_OFFSET (memory_start >> PAGE_SHIFT)
+
+#define __pa(virt)  ((unsigned long) (virt))
+#define __va(phys) ((void *)(phys))
+
+#define virt_to_pfn(kaddr)	(__pa(kaddr) >> PAGE_SHIFT)
+
+#define phys_to_pfn(p) PHYS_PFN(p)
+#define pfn_to_phys(pfn) PFN_PHYS(pfn)
+
+#define virt_addr_valid(v) pfn_valid(phys_to_pfn(__pa(v)))
+
+#endif // __ASSEMBLY__
+
+#include <asm-generic/memory_model.h>
+#include <asm-generic/getorder.h>
+
+#endif // _ASM_LKL_PAGE_MMU_H

arch/lkl/include/asm/page.h

@@ -1,15 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _ASM_LKL_PAGE_H
 #define _ASM_LKL_PAGE_H
 
+#ifndef CONFIG_MMU
 #define ARCH_PFN_OFFSET	(memory_start >> PAGE_SHIFT)
+#include <asm-generic/page.h>
+#else // CONFIG_MMU
+#include <asm/page-mmu.h>
+#endif // CONFIG_MMU
 
 #ifndef __ASSEMBLY__
 void free_mem(void);
 void bootmem_init(unsigned long mem_size);
 #endif
 
-#include <asm-generic/page.h>
-
 #undef PAGE_OFFSET
 #define PAGE_OFFSET memory_start
 

arch/lkl/include/asm/pgalloc.h

@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LKL_PGALLOC_H
+#define _LKL_PGALLOC_H
+
+#include <linux/mm.h>
+#include <linux/mmzone.h>
+
+#include <asm-generic/pgalloc.h>
+
+#ifdef CONFIG_MMU
+
+static inline void pmd_populate_kernel(struct mm_struct *mm,
+			pmd_t *pmd, pte_t *pte)
+{
+	set_pmd(pmd, __pmd(_PAGE_TABLE + (unsigned long) __pa(pte)));
+}
+
+static inline void pmd_populate(struct mm_struct *mm,
+			pmd_t *pmd, pgtable_t pte)
+{
+	set_pmd(pmd, __pmd(_PAGE_TABLE + (page_to_pfn(pte) << PAGE_SHIFT)));
+}
+
+#define pmd_pgtable(pmd) pmd_page(pmd)
+
+extern pgd_t *pgd_alloc(struct mm_struct *mm);
+
+#define __pte_free_tlb(tlb, pte, address) tlb_remove_page((tlb), (pte))
+
+#define __pmd_free_tlb(tlb, pmd, address)			\
+do {								\
+	pagetable_pmd_dtor(virt_to_ptdesc(pmd));			\
+	tlb_remove_page_ptdesc((tlb), virt_to_ptdesc(pmd));	\
+} while (0)
+
+#endif // CONFIG_MMU
+
+#endif /* _LKL_PGALLOC_H */