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From:   Anup Patel <Anup.Patel@wdc.com>
To:     Palmer Dabbelt <palmer@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>
CC:     Atish Patra <Atish.Patra@wdc.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Christoph Hellwig <hch@infradead.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Anup Patel <Anup.Patel@wdc.com>
Subject: [PATCH 2/3] RISC-V: Make setup_vm() independent of GCC code model
Thread-Topic: [PATCH 2/3] RISC-V: Make setup_vm() independent of GCC code
 model
Thread-Index: AQHU2SAXFOwCqD7TIUe3nwMe83Le9Q==
Date:   Tue, 12 Mar 2019 22:08:16 +0000
Message-ID: <20190312220752.128141-3-anup.patel@wdc.com>
References: <20190312220752.128141-1-anup.patel@wdc.com>
In-Reply-To: <20190312220752.128141-1-anup.patel@wdc.com>
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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=3Dmedany 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=3Dmedlow 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=3Dmedlow but it works perfectly fine
for cmodel=3Dmedany.

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@wdc.com>
---
 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:
=20
 	/* Initialize page tables and relocate to virtual addresses */
 	la sp, init_thread_union + THREAD_SIZE
+	la a0, _start
 	call setup_vm
 	call relocate
=20
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)
 	}
 }
=20
-asmlinkage void __init setup_vm(void)
+static inline void *__early_va(void *ptr, uintptr_t load_pa)
 {
 	extern char _start;
+	uintptr_t va =3D (uintptr_t)ptr;
+	uintptr_t sz =3D (uintptr_t)(&_end) - (uintptr_t)(&_start);
+
+	if (va >=3D 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 =3D (uintptr_t) &_start;
+#ifndef __PAGETABLE_PMD_FOLDED
+	pmd_t *pmdp;
+#endif
+	pgd_t *pgdp;
+	phys_addr_t map_pa;
+	pgprot_t tableprot =3D __pgprot(_PAGE_TABLE);
 	pgprot_t prot =3D __pgprot(pgprot_val(PAGE_KERNEL) | _PAGE_EXEC);
=20
-	va_pa_offset =3D PAGE_OFFSET - pa;
-	pfn_base =3D PFN_DOWN(pa);
+	va_pa_offset =3D PAGE_OFFSET - load_pa;
+	pfn_base =3D PFN_DOWN(load_pa);
=20
 	/* Sanity check alignment and size */
 	BUG_ON((PAGE_OFFSET % PGDIR_SIZE) !=3D 0);
-	BUG_ON((pa % (PAGE_SIZE * PTRS_PER_PTE)) !=3D 0);
+	BUG_ON((load_pa % (PAGE_SIZE * PTRS_PER_PTE)) !=3D 0);
=20
 #ifndef __PAGETABLE_PMD_FOLDED
-	trampoline_pg_dir[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =3D
-		pfn_pgd(PFN_DOWN((uintptr_t)trampoline_pmd),
-			__pgprot(_PAGE_TABLE));
-	trampoline_pmd[0] =3D pfn_pmd(PFN_DOWN(pa), prot);
+	pgdp =3D __early_va(trampoline_pg_dir, load_pa);
+	map_pa =3D (uintptr_t)__early_va(trampoline_pmd, load_pa);
+	pgdp[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =3D
+		pfn_pgd(PFN_DOWN(map_pa), tableprot);
+	trampoline_pmd[0] =3D pfn_pmd(PFN_DOWN(load_pa), prot);
+
+	pgdp =3D __early_va(swapper_pg_dir, load_pa);
=20
 	for (i =3D 0; i < (-PAGE_OFFSET)/PGDIR_SIZE; ++i) {
 		size_t o =3D (PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
=20
-		swapper_pg_dir[o] =3D
-			pfn_pgd(PFN_DOWN((uintptr_t)swapper_pmd) + i,
-				__pgprot(_PAGE_TABLE));
+		map_pa =3D (uintptr_t)__early_va(swapper_pmd, load_pa);
+		pgdp[o] =3D pfn_pgd(PFN_DOWN(map_pa) + i, tableprot);
 	}
+	pmdp =3D __early_va(swapper_pmd, load_pa);
 	for (i =3D 0; i < ARRAY_SIZE(swapper_pmd); i++)
-		swapper_pmd[i] =3D pfn_pmd(PFN_DOWN(pa + i * PMD_SIZE), prot);
+		pmdp[i] =3D pfn_pmd(PFN_DOWN(load_pa + i * PMD_SIZE), prot);
=20
-	swapper_pg_dir[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =3D
-		pfn_pgd(PFN_DOWN((uintptr_t)fixmap_pmd),
-				__pgprot(_PAGE_TABLE));
+	map_pa =3D (uintptr_t)__early_va(fixmap_pmd, load_pa);
+	pgdp[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =3D
+		pfn_pgd(PFN_DOWN(map_pa), tableprot);
+	pmdp =3D __early_va(fixmap_pmd, load_pa);
+	map_pa =3D (uintptr_t)__early_va(fixmap_pte, load_pa);
 	fixmap_pmd[(FIXADDR_START >> PMD_SHIFT) % PTRS_PER_PMD] =3D
-		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] =3D
-		pfn_pgd(PFN_DOWN(pa), prot);
+	pgdp =3D __early_va(trampoline_pg_dir, load_pa);
+	pgdp[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =3D
+		pfn_pgd(PFN_DOWN(load_pa), prot);
+
+	pgdp =3D __early_va(swapper_pg_dir, load_pa);
=20
 	for (i =3D 0; i < (-PAGE_OFFSET)/PGDIR_SIZE; ++i) {
 		size_t o =3D (PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
=20
-		swapper_pg_dir[o] =3D
-			pfn_pgd(PFN_DOWN(pa + i * PGDIR_SIZE), prot);
+		pgdp[o] =3D pfn_pgd(PFN_DOWN(load_pa + i * PGDIR_SIZE), prot);
 	}
=20
-	swapper_pg_dir[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =3D
-		pfn_pgd(PFN_DOWN((uintptr_t)fixmap_pte),
-				__pgprot(_PAGE_TABLE));
+	map_pa =3D (uintptr_t)__early_va(fixmap_pte, load_pa);
+	pgdp[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =3D
+		pfn_pgd(PFN_DOWN(map_pa), tableprot);
 #endif
 }
--=20
2.17.1