linux-kernel - Re: [PATCHv2] x86/boot/KASLR: skip the specified crashkernel reserved region

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Date:   Fri, 22 Mar 2019 16:34:19 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Pingfan Liu <kernelfans@...il.com>, dyoung@...hat.com
Cc:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Will Deacon <will.deacon@....com>,
        Nicolas Pitre <nico@...aro.org>,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2] x86/boot/KASLR: skip the specified crashkernel
 reserved region

On 03/22/19 at 03:52pm, Baoquan He wrote:
> On 03/22/19 at 03:43pm, Pingfan Liu wrote:
> > > > +/* parse crashkernel=x@y option */
> > > > +static void mem_avoid_crashkernel_simple(char *option)
> > >
> > > Chao ever mentioned this, I want to ask again, why does it has to be
> > > xxx_simple()?
> > >
> > Seems that I had replied Chao's question in another email. The naming
> > follows the function parse_crashkernel_simple(), as the notes above
>                        ~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Sorry, I don't get.  typo?

OK, I misunderstood it. We do have parse_crashkernel_simple() to handle 
crashkernel=size[@offset] case, to differente with other complicated
cases, like crashkernel=size,[high|low],

Then I am fine with this naming. Soryy about the noise.

By the way, do you think if we should take care of this case:
crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]

It can also specify @offset. Not sure if it's too complicated, you may
have a investigation.

These two cases have dependency on your crashkernel=X bug fix patch.
The current code only allow crashkernel= to reserve under 896MB. I
noticed Boris has agreed on the solution. Maybe you can repost a new
version based on the discussion.

http://lkml.kernel.org/r/1548047768-7656-1-git-send-email-kernelfans@gmail.com
[PATCHv7] x86/kdump: bugfix, make the behavior of crashkernel=X consistent with kaslr

Thanks
Baoquan

> 
> > the definition
> > /*
> >  * That function parses "simple" (old) crashkernel command lines like
> >  *
> >  * crashkernel=size[@offset]
> 
> Hmm, should only crashkernel=size@...set be cared? crashkernel=size will
> auto finding a place to reserve, and that is after KASLR.
> 
> >  *
> >  * It returns 0 on success and -EINVAL on failure.
> >  */
> > static int __init parse_crashkernel_simple(char *cmdline,
> > 
> > Do you have alternative suggestion?
> > 
> > > Except of these, patch looks good to me. It's a nice catch, and only
> > > need a simple fix based on the current code.
> > >
> > Thank you for the kindly review.
> > 
> > Regards,
> > Pingfan
> > 
> > > Thanks
> > > Baoquan
> > >
> > > > +{
> > > > +     unsigned long long crash_size, crash_base;
> > > > +     char *cur = option;
> > > > +
> > > > +     crash_size = memparse(option, &cur);
> > > > +     if (option == cur)
> > > > +             return;
> > > > +
> > > > +     if (*cur == '@') {
> > > > +             option = cur + 1;
> > > > +             crash_base = memparse(option, &cur);
> > > > +             if (option == cur)
> > > > +                     return;
> > > > +             mem_avoid[MEM_AVOID_CRASHKERNEL].start = crash_base;
> > > > +             mem_avoid[MEM_AVOID_CRASHKERNEL].size = crash_size;
> > > > +     }
> > > > +}
> > > >
> > > >  static void handle_mem_options(void)
> > > >  {
> > > > @@ -250,7 +270,7 @@ static void handle_mem_options(void)
> > > >       u64 mem_size;
> > > >
> > > >       if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
> > > > -             !strstr(args, "hugepages"))
> > > > +             !strstr(args, "hugepages") && !strstr(args, "crashkernel="))
> > > >               return;
> > > >
> > > >       tmp_cmdline = malloc(len + 1);
> > > > @@ -286,6 +306,8 @@ static void handle_mem_options(void)
> > > >                               goto out;
> > > >
> > > >                       mem_limit = mem_size;
> > > > +             } else if (strstr(param, "crashkernel")) {
> > > > +                     mem_avoid_crashkernel_simple(val);
> > > >               }
> > > >       }
> > > >
> > > > @@ -414,7 +436,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
> > > >
> > > >       /* We don't need to set a mapping for setup_data. */
> > > >
> > > > -     /* Mark the memmap regions we need to avoid */
> > > > +     /* Mark the regions we need to avoid */
> > > >       handle_mem_options();
> > > >
> > > >  #ifdef CONFIG_X86_VERBOSE_BOOTUP
> > > > --
> > > > 2.7.4
> > > >