linux-kernel - Re: [PATCHv3] x86/boot/KASLR: skip the specified crashkernel region

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Message-ID: <20190402065245.GN7627@MiWiFi-R3L-srv>
Date:   Tue, 2 Apr 2019 14:52:45 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     Pingfan Liu <kernelfans@...il.com>, 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>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3] x86/boot/KASLR: skip the specified crashkernel region

On 04/02/19 at 02:19pm, Chao Fan wrote:
> On Tue, Apr 02, 2019 at 12:10:46PM +0800, Pingfan Liu wrote:
> >crashkernel=x@y or or =range1:size1[,range2:size2,...]@offset option may
> or or?
> >fail to reserve the required memory region if KASLR puts kernel into the
> >region. To avoid this uncertainty, asking KASLR to skip the required
> >region.
> >
> >Signed-off-by: Pingfan Liu <kernelfans@...il.com>
> >Cc: Thomas Gleixner <tglx@...utronix.de>
> >Cc: Ingo Molnar <mingo@...hat.com>
> >Cc: Borislav Petkov <bp@...en8.de>
> >Cc: "H. Peter Anvin" <hpa@...or.com>
> >Cc: Baoquan He <bhe@...hat.com>
> >Cc: Will Deacon <will.deacon@....com>
> >Cc: Nicolas Pitre <nico@...aro.org>
> >Cc: Pingfan Liu <kernelfans@...il.com>
> >Cc: Chao Fan <fanc.fnst@...fujitsu.com>
> >Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> >Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> >Cc: linux-kernel@...r.kernel.org
> >---
> [...]
> >+
> >+/* handle crashkernel=x@y or =range1:size1[,range2:size2,...]@offset options */
> 
> Before review, I want to say more about the background.
> It's very hard to review the code for someone who is not so familiar
> with kdump, so could you please explain more ahout
> the uasge of crashkernel=range1:size1[,range2:size2,...]@offset.
> And also there are so many jobs who are parsing string. So I really
> need your help to understand the PATCH.

The hard part may be handle_crashkernel_mem() itself. However, it's
almost copied from parse_crashkernel_mem() completely. If we can reuse
that function, thing's gonna be perfect.

> 
> >+static void mem_avoid_specified_crashkernel_region(char *option)
> >+{
> >+	unsigned long long crash_size, crash_base = 0;
> >+	char	*first_colon, *first_space, *cur = option;
> Is there a tab after char?
> >+
> >+	first_colon = strchr(option, ':');
> >+	first_space = strchr(option, ' ');
> >+	/* if contain ":" */
> >+	if (first_colon && (!first_space || first_colon < first_space)) {
> >+		int i;
> >+		u64 total_sz = 0;
> >+		struct boot_e820_entry *entry;
> >+
> >+		for (i = 0; i < boot_params->e820_entries; i++) {
> >+			entry = &boot_params->e820_table[i];
> >+			/* Skip non-RAM entries. */
> >+			if (entry->type != E820_TYPE_RAM)
> >+				continue;
> >+			total_sz += entry->size;
> I wonder whether it's needed to consider the memory ranges here.
> I think it's OK to only record the regions should to be avoid.
> I remeber I ever talked with Baoquan about the similiar problems.
> @Baoquan, I am not sure if I misunderstand something.

Not sure if I get you. Could you be more specific?