Re: [PATCH v4 1/3] riscv: Move kernel mapping outside of linear mapping

From: Guenter Roeck <linux@roeck-us.net>
To: Alexandre Ghiti <alex@ghiti.fr>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Arnd Bergmann <arnd@arndb.de>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Alexander Potapenko <glider@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	linux-doc@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
	linux-arch@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v4 1/3] riscv: Move kernel mapping outside of linear mapping
Date: Fri, 16 Apr 2021 11:51:39 -0700	[thread overview]
Message-ID: <20210416185139.GA42339@roeck-us.net> (raw)
In-Reply-To: <20210409061500.14673-2-alex@ghiti.fr>

On Fri, Apr 09, 2021 at 02:14:58AM -0400, Alexandre Ghiti wrote:
> 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>

In next-20210416, when booting a riscv32 image in qemu, this patch results in:

[    0.000000] Linux version 5.12.0-rc7-next-20210416 (groeck@desktop) (riscv32-linux-gcc (GCC) 10.3.0, GNU ld (GNU Binutils) 2.36.1) #1 SMP Fri Apr 16 10:38:09 PDT 2021
[    0.000000] OF: fdt: Ignoring memory block 0x80000000 - 0xa0000000
[    0.000000] Machine model: riscv-virtio,qemu
[    0.000000] earlycon: uart8250 at MMIO 0x10000000 (options '115200')
[    0.000000] printk: bootconsole [uart8250] enabled
[    0.000000] efi: UEFI not found.
[    0.000000] Kernel panic - not syncing: init_resources: Failed to allocate 160 bytes
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.12.0-rc7-next-20210416 #1
[    0.000000] Hardware name: riscv-virtio,qemu (DT)
[    0.000000] Call Trace:
[    0.000000] [<80005292>] walk_stackframe+0x0/0xce
[    0.000000] [<809f4db8>] dump_backtrace+0x38/0x46
[    0.000000] [<809f4dd4>] show_stack+0xe/0x16
[    0.000000] [<809ff1d0>] dump_stack+0x92/0xc6
[    0.000000] [<809f4fee>] panic+0x10a/0x2d8
[    0.000000] [<80c02b24>] setup_arch+0x2a0/0x4ea
[    0.000000] [<80c006b0>] start_kernel+0x90/0x628
[    0.000000] ---[ end Kernel panic - not syncing: init_resources: Failed to allocate 160 bytes ]---

Reverting it fixes the problem. I understand that the version in -next is
different to this version of the patch, but I also tried v4 and it still
crashes with the same error message.

Guenter