Subject: [PATCH v26 3/7] arm64: kdump: add kdump support

From: [email-masked] (James Morse)
Date: Fri, 16 Sep 2016 15:50:24 +0100

On 07/09/16 05:29, AKASHI Takahiro wrote:
> On crash dump kernel, all the information about primary kernel's system
> memory (core image) is available in elf core header.
> The primary kernel will set aside this header with reserve_elfcorehdr()
> at boot time and inform crash dump kernel of its location via a new
> device-tree property, "linux,elfcorehdr".
> 
> Please note that all other architectures use traditional "elfcorehdr="
> kernel parameter for this purpose.
> 
> Then crash dump kernel will access the primary kernel's memory with
> copy_oldmem_page(), which reads one page by ioremap'ing it since it does
> not reside in linear mapping on crash dump kernel.
> 
> We also need our own elfcorehdr_read() here since the header is placed
> within crash dump kernel's usable memory.

One nit below, looks good.

Reviewed-by: James Morse <[email-masked]>

Thanks,

James

> diff --git a/arch/arm64/kernel/crash_dump.c b/arch/arm64/kernel/crash_dump.c

> +/**
> + * copy_oldmem_page() - copy one page from old kernel memory
> + * @pfn: page frame number to be copied
> + * @buf: buffer where the copied page is placed
> + * @csize: number of bytes to copy
> + * @offset: offset in bytes into the page
> + * @userbuf: if set, @buf is in a user address space
> + *
> + * This function copies one page from old kernel memory into buffer pointed by
> + * @buf. If @buf is in userspace, set @userbuf to %1. Returns number of bytes
> + * copied or negative error in case of failure.
> + */
> +ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
> +			 size_t csize, unsigned long offset,
> +			 int userbuf)
> +{
> +	void *vaddr;
> +
> +	if (!csize)
> +		return 0;
> +
> +	vaddr = memremap(__pfn_to_phys(pfn), PAGE_SIZE, MEMREMAP_WB);
> +	if (!vaddr)
> +		return -ENOMEM;
> +
> +	if (userbuf) {

> +		if (copy_to_user(buf, vaddr + offset, csize)) {

If you re-cast buf with (char __user *), it should stop sparse complaining:
> ../arch/arm64/kernel/crash_dump.c:45:34: warning: incorrect type in argument 1
(different address spaces)
> ../arch/arm64/kernel/crash_dump.c:45:34:    expected void [noderef] <asn:1>*to
> ../arch/arm64/kernel/crash_dump.c:45:34:    got char *buf