Re: [PATCH] arm64: mm: Set MAX_PHYSMEM_BITS based on ARM64_VA_BITS

[Robin Murphy]

On 09/11/17 22:58, Krishna Reddy wrote:
> MAX_PHYSMEM_BITS greater than ARM64_VA_BITS is causing memory
> access fault, when HMM_DMIRROR test is enabled.
> In the failing case, ARM64_VA_BITS=39 and MAX_PHYSMEM_BITS=48.
> HMM_DMIRROR test selects phys memory range from end based on
> MAX_PHYSMEM_BITS and gets mapped into VA space linearly.
> As VA space is 39-bit and phys space is 48-bit, this has caused
> incorrect mapping and leads to memory access fault.
>
> Limiting the MAX_PHYSMEM_BITS to ARM64_VA_BITS fixes the issue and is
> the right thing instead of hard coding it as 48-bit always.
>
> [    3.378655] Unable to handle kernel paging request at virtual address 3befd000000
> [    3.378662] pgd = ffffff800a04b000
> [    3.378900] [3befd000000] *pgd=0000000081fa3003, *pud=0000000081fa3003, *pmd=0060000268200711
> [    3.378933] Internal error: Oops: 96000044 [#1] PREEMPT SMP
> [    3.378938] Modules linked in:
> [    3.378948] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.9.52-tegra-g91402fdc013b-dirty #51
> [    3.378950] Hardware name: quill (DT)
> [    3.378954] task: ffffffc1ebac0000 task.stack: ffffffc1eba64000
> [    3.378967] PC is at __memset+0x1ac/0x1d0
> [    3.378976] LR is at sparse_add_one_section+0xf8/0x174
> [    3.378981] pc : [<ffffff80084c212c>] lr : [<ffffff8008eda17c>] pstate: 404000c5
> [    3.378983] sp : ffffffc1eba67a40
> [    3.378993] x29: ffffffc1eba67a40 x28: 0000000000000000
> [    3.378999] x27: 000000000003ffff x26: 0000000000000040
> [    3.379005] x25: 00000000000003ff x24: ffffffc1e9f6cf80
> [    3.379010] x23: ffffff8009ecb2d4 x22: 000003befd000000
> [    3.379015] x21: ffffffc1e9923ff0 x20: 000000000003ffff
> [    3.379020] x19: 00000000ffffffef x18: ffffffffffffffff
> [    3.379025] x17: 00000000000024d7 x16: 0000000000000000
> [    3.379030] x15: ffffff8009cd8690 x14: ffffffc1e9f6c70c
> [    3.379035] x13: ffffffc1e9f6c70b x12: 0000000000000030
> [    3.379039] x11: 0000000000000040 x10: 0101010101010101
> [    3.379044] x9 : 0000000000000000 x8 : 000003befd000000
> [    3.379049] x7 : 0000000000000000 x6 : 000000000000003f
> [    3.379053] x5 : 0000000000000040 x4 : 0000000000000000
> [    3.379058] x3 : 0000000000000004 x2 : 0000000000ffffc0
> [    3.379063] x1 : 0000000000000000 x0 : 000003befd000000
> [    3.379064]
> [    3.379069] Process swapper/0 (pid: 1, stack limit = 0xffffffc1eba64028)
> [    3.379071] Call trace:
> [    3.379079] [<ffffff80084c212c>] __memset+0x1ac/0x1d0

What's the deal with this memset? AFAICS we're in __add_pages() from 
hmm_devmem_pages_create() calling add_pages() for private memory which 
it does not expect to be in the linear map anyway :/

There appears to be a more fundamental problem being papered over here.

Robin.

> [    3.379085] [<ffffff8008ed5100>] __add_pages+0x130/0x2e0
> [    3.379093] [<ffffff8008211cf4>] hmm_devmem_pages_create+0x20c/0x310
> [    3.379100] [<ffffff8008211fcc>] hmm_devmem_add+0x1d4/0x270
> [    3.379128] [<ffffff80087111c8>] dmirror_probe+0x50/0x158
> [    3.379137] [<ffffff8008732590>] platform_drv_probe+0x60/0xc8
> [    3.379143] [<ffffff800872fbf4>] driver_probe_device+0x26c/0x420
> [    3.379149] [<ffffff800872fecc>] __driver_attach+0x124/0x128
> [    3.379155] [<ffffff800872d388>] bus_for_each_dev+0x88/0xe8
> [    3.379166] [<ffffff800872f248>] driver_attach+0x30/0x40
> [    3.379171] [<ffffff800872ec18>] bus_add_driver+0x1f8/0x2b0
> [    3.379177] [<ffffff8008730e38>] driver_register+0x68/0x100
> [    3.379183] [<ffffff80087324d4>] __platform_driver_register+0x5c/0x68
> [    3.379192] [<ffffff800951f918>] hmm_dmirror_init+0x88/0xc4
> [    3.379200] [<ffffff800808359c>] do_one_initcall+0x5c/0x170
> [    3.379208] [<ffffff80094e0dd0>] kernel_init_freeable+0x1b8/0x258
> [    3.379231] [<ffffff8008ed44f0>] kernel_init+0x18/0x108
> [    3.379236] [<ffffff80080832d0>] ret_from_fork+0x10/0x40
> [    3.379246] ---[ end trace 578db63bb139b8b8 ]---
>
> Signed-off-by: Krishna Reddy <vdumpa@xxxxxxxxxx>
> ---
>   arch/arm64/include/asm/sparsemem.h | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm64/include/asm/sparsemem.h b/arch/arm64/include/asm/sparsemem.h
> index 74a9d301819f..19ecd0b0f3a3 100644
> --- a/arch/arm64/include/asm/sparsemem.h
> +++ b/arch/arm64/include/asm/sparsemem.h
> @@ -17,7 +17,13 @@
>   #define __ASM_SPARSEMEM_H
>   
>   #ifdef CONFIG_SPARSEMEM
> +
> +#ifdef CONFIG_ARM64_VA_BITS
> +#define MAX_PHYSMEM_BITS	CONFIG_ARM64_VA_BITS
> +#else
>   #define MAX_PHYSMEM_BITS	48
> +#endif
> +
>   #define SECTION_SIZE_BITS	30
>   #endif
>