riscv: Move kernel mapping outside of linear mapping

This is a preparatory patch for relocatable kernel and sv48 support.

The kernel used to be linked at PAGE_OFFSET address therefore we could use
the linear mapping for the kernel mapping. But the relocated kernel base
address will be different from PAGE_OFFSET and since in the linear mapping,
two different virtual addresses cannot point to the same physical address,
the kernel mapping needs to lie outside the linear mapping so that we don't
have to copy it at the same physical offset.

The kernel mapping is moved to the last 2GB of the address space, BPF
is now always after the kernel and modules use the 2GB memory range right
before the kernel, so BPF and modules regions do not overlap. KASLR
implementation will simply have to move the kernel in the last 2GB range
and just take care of leaving enough space for BPF.

In addition, by moving the kernel to the end of the address space, both
sv39 and sv48 kernels will be exactly the same without needing to be
relocated at runtime.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
[Palmer: Squash the STRICT_RWX fix, and a !MMU fix]
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 8f17519208c7..1b14d523a95c 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -231,6 +231,19 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 		return;
 	}
 
+#ifdef CONFIG_64BIT
+	/*
+	 * Modules in 64bit kernels lie in their own virtual region which is not
+	 * in the vmalloc region, but dealing with page faults in this region
+	 * or the vmalloc region amounts to doing the same thing: checking that
+	 * the mapping exists in init_mm.pgd and updating user page table, so
+	 * just use vmalloc_fault.
+	 */
+	if (unlikely(addr >= MODULES_VADDR && addr < MODULES_END)) {
+		vmalloc_fault(regs, code, addr);
+		return;
+	}
+#endif
 	/* Enable interrupts if they were enabled in the parent context. */
 	if (likely(regs->status & SR_PIE))
 		local_irq_enable();