[PATCH 2/3] RISC-V: Make setup_vm() independent of GCC code model

[Anup Patel]

The setup_vm() must access kernel symbols in a position independent way
because it will be called from head.S with MMU off.

If we compile kernel with cmodel=medany then PC-relative addressing will
be used in setup_vm() to access kernel symbols so it works perfectly fine.

Although, if we compile kernel with cmodel=medlow then either absolute
addressing or PC-relative addressing (based on whichever requires fewer
instructions) is used to access kernel symbols in setup_vm(). This can
break setup_vm() whenever any absolute addressing is used to access
kernel symbols.

With the movement of setup_vm() from kernel/setup.c to mm/init.c, the
setup_vm() is now broken for cmodel=medlow but it works perfectly fine
for cmodel=medany.

This patch fixes setup_vm() and makes it independent of GCC code model
by accessing kernel symbols relative to kernel load address instead of
assuming PC-relative addressing.

Fixes: 6f1e9e946f0b ("RISC-V: Move setup_vm() to mm/init.c")
Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
---
 arch/riscv/kernel/head.S |  1 +
 arch/riscv/mm/init.c     | 71 ++++++++++++++++++++++++++--------------
 2 files changed, 47 insertions(+), 25 deletions(-)

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index fe884cd69abd..7966262b4f9d 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -62,6 +62,7 @@ clear_bss_done:
 
 	/* Initialize page tables and relocate to virtual addresses */
 	la sp, init_thread_union + THREAD_SIZE
+	la a0, _start
 	call setup_vm
 	call relocate
 
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index b379a75ac6a6..f35299f2f3d5 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -172,55 +172,76 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
 	}
 }
 
-asmlinkage void __init setup_vm(void)
+static inline void *__early_va(void *ptr, uintptr_t load_pa)
 {
 	extern char _start;
+	uintptr_t va = (uintptr_t)ptr;
+	uintptr_t sz = (uintptr_t)(&_end) - (uintptr_t)(&_start);
+
+	if (va >= PAGE_OFFSET && va < (PAGE_OFFSET + sz))
+		return (void *)(load_pa + (va - PAGE_OFFSET));
+	return (void *)va;
+}
+
+asmlinkage void __init setup_vm(uintptr_t load_pa)
+{
 	uintptr_t i;
-	uintptr_t pa = (uintptr_t) &_start;
+#ifndef __PAGETABLE_PMD_FOLDED
+	pmd_t *pmdp;
+#endif
+	pgd_t *pgdp;
+	phys_addr_t map_pa;
+	pgprot_t tableprot = __pgprot(_PAGE_TABLE);
 	pgprot_t prot = __pgprot(pgprot_val(PAGE_KERNEL) | _PAGE_EXEC);
 
-	va_pa_offset = PAGE_OFFSET - pa;
-	pfn_base = PFN_DOWN(pa);
+	va_pa_offset = PAGE_OFFSET - load_pa;
+	pfn_base = PFN_DOWN(load_pa);
 
 	/* Sanity check alignment and size */
 	BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
-	BUG_ON((pa % (PAGE_SIZE * PTRS_PER_PTE)) != 0);
+	BUG_ON((load_pa % (PAGE_SIZE * PTRS_PER_PTE)) != 0);
 
 #ifndef __PAGETABLE_PMD_FOLDED
-	trampoline_pg_dir[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =
-		pfn_pgd(PFN_DOWN((uintptr_t)trampoline_pmd),
-			__pgprot(_PAGE_TABLE));
-	trampoline_pmd[0] = pfn_pmd(PFN_DOWN(pa), prot);
+	pgdp = __early_va(trampoline_pg_dir, load_pa);
+	map_pa = (uintptr_t)__early_va(trampoline_pmd, load_pa);
+	pgdp[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =
+		pfn_pgd(PFN_DOWN(map_pa), tableprot);
+	trampoline_pmd[0] = pfn_pmd(PFN_DOWN(load_pa), prot);
+
+	pgdp = __early_va(swapper_pg_dir, load_pa);
 
 	for (i = 0; i < (-PAGE_OFFSET)/PGDIR_SIZE; ++i) {
 		size_t o = (PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
 
-		swapper_pg_dir[o] =
-			pfn_pgd(PFN_DOWN((uintptr_t)swapper_pmd) + i,
-				__pgprot(_PAGE_TABLE));
+		map_pa = (uintptr_t)__early_va(swapper_pmd, load_pa);
+		pgdp[o] = pfn_pgd(PFN_DOWN(map_pa) + i, tableprot);
 	}
+	pmdp = __early_va(swapper_pmd, load_pa);
 	for (i = 0; i < ARRAY_SIZE(swapper_pmd); i++)
-		swapper_pmd[i] = pfn_pmd(PFN_DOWN(pa + i * PMD_SIZE), prot);
+		pmdp[i] = pfn_pmd(PFN_DOWN(load_pa + i * PMD_SIZE), prot);
 
-	swapper_pg_dir[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =
-		pfn_pgd(PFN_DOWN((uintptr_t)fixmap_pmd),
-				__pgprot(_PAGE_TABLE));
+	map_pa = (uintptr_t)__early_va(fixmap_pmd, load_pa);
+	pgdp[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =
+		pfn_pgd(PFN_DOWN(map_pa), tableprot);
+	pmdp = __early_va(fixmap_pmd, load_pa);
+	map_pa = (uintptr_t)__early_va(fixmap_pte, load_pa);
 	fixmap_pmd[(FIXADDR_START >> PMD_SHIFT) % PTRS_PER_PMD] =
-		pfn_pmd(PFN_DOWN((uintptr_t)fixmap_pte),
-				__pgprot(_PAGE_TABLE));
+		pfn_pmd(PFN_DOWN(map_pa), tableprot);
 #else
-	trampoline_pg_dir[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =
-		pfn_pgd(PFN_DOWN(pa), prot);
+	pgdp = __early_va(trampoline_pg_dir, load_pa);
+	pgdp[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =
+		pfn_pgd(PFN_DOWN(load_pa), prot);
+
+	pgdp = __early_va(swapper_pg_dir, load_pa);
 
 	for (i = 0; i < (-PAGE_OFFSET)/PGDIR_SIZE; ++i) {
 		size_t o = (PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
 
-		swapper_pg_dir[o] =
-			pfn_pgd(PFN_DOWN(pa + i * PGDIR_SIZE), prot);
+		pgdp[o] = pfn_pgd(PFN_DOWN(load_pa + i * PGDIR_SIZE), prot);
 	}
 
-	swapper_pg_dir[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =
-		pfn_pgd(PFN_DOWN((uintptr_t)fixmap_pte),
-				__pgprot(_PAGE_TABLE));
+	map_pa = (uintptr_t)__early_va(fixmap_pte, load_pa);
+	pgdp[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =
+		pfn_pgd(PFN_DOWN(map_pa), tableprot);
 #endif
 }
-- 
2.17.1