linux-kernel - Re: [tip:x86/mm] kdump, proc/vmcore: Enable kdumping encrypted memory with SME enabled

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Message-ID: <8147597a-f8e0-7f1a-bd2b-e914b18c5c74@redhat.com>
Date:   Mon, 8 Oct 2018 16:47:34 +0800
From:   lijiang <lijiang@...hat.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org, tglx@...utronix.de,
        hpa@...or.com, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] kdump, proc/vmcore: Enable kdumping encrypted memory
 with SME enabled

在 2018年10月08日 16:00, Borislav Petkov 写道:
> On Mon, Oct 08, 2018 at 03:11:56PM +0800, lijiang wrote:
>> I used this ".config" to compile kernel in the attachment, and got a compile error.
>> Would you like to have a try?
>>
>> [root@...dl385g10-03 linux]# make ARCH=i386 -j32
>>   ......
>>   LD      vmlinux.o
>>   MODPOST vmlinux.o
>> fs/proc/vmcore.o：In function ‘read_from_oldmem’：
>> /home/linux/fs/proc/vmcore.c:127：undefined reference to ‘copy_oldmem_page_encrypted’
>> make: *** [vmlinux] error 1
> 
> Thanks, that triggered here. Ok, I guess something like this, to avoid
> the ugly ifdeffery:
> 
> ---
> diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
> index 33ee47670b99..8696800f2eea 100644
> --- a/arch/x86/kernel/crash_dump_32.c
> +++ b/arch/x86/kernel/crash_dump_32.c
> @@ -80,6 +80,16 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
>  	return csize;
>  }
>  
> +/*
> + * 32-bit parrot version to avoid build errors.
> + */
> +ssize_t copy_oldmem_page_encrypted(unsigned long pfn, char *buf, size_t csize,
> +				   unsigned long offset, int userbuf)
> +{
> +	WARN_ON_ONCE(1);
> +	return copy_oldmem_page(pfn, buf, csize, offset, userbuf);
> +}
> +

It looks like a good way to avoid the 'ifdefined', and it's also good enough for i386.

But for other architectures, such as POWERPC/ARM..., we will also have to add the same 
function for every architecture. Otherwise, i guess that they also have a same compile
error on other architectures.

Sometimes, it's hard to make a choice.

Regards,
Lianbo
>  static int __init kdump_buf_page_init(void)
>  {
>  	int ret = 0;
> 
> 
>