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

[Pingfan Liu <kernelfans@gmail.com>]

On Tue, Apr 2, 2019 at 1:20 PM Chao Fan <fanc.fnst@cn.fujitsu.com> 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@gmail.com>
> >Cc: Thomas Gleixner <tglx@linutronix.de>
> >Cc: Ingo Molnar <mingo@redhat.com>
> >Cc: Borislav Petkov <bp@alien8.de>
> >Cc: "H. Peter Anvin" <hpa@zytor.com>
> >Cc: Baoquan He <bhe@redhat.com>
> >Cc: Will Deacon <will.deacon@arm.com>
> >Cc: Nicolas Pitre <nico@linaro.org>
> >Cc: Pingfan Liu <kernelfans@gmail.com>
> >Cc: Chao Fan <fanc.fnst@cn.fujitsu.com>
> >Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> >Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> >Cc: linux-kernel@vger.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.
>
> >+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.
Maybe not catch you exactly. In the case of
crashkernel=range1:size1[,range2:size2,...]@offset, the size of avoid
region depends on the size of total system ram.
> I remeber I ever talked with Baoquan about the similiar problems.
> @Baoquan, I am not sure if I misunderstand something.
>
> Thanks,
> Chao Fan
> >+              }
> >+              handle_crashkernel_mem(option, total_sz, &crash_size,
> >+                      &crash_base);
> >+      } else {
> >+              crash_size = memparse(option, &cur);
> >+              if (option == cur)
> >+                      return;
> >+              while (*cur && *cur != ' ' && *cur != '@')
> >+                      cur++;
> >+              if (*cur == '@') {
> >+                      option = cur + 1;
> >+                      crash_base = memparse(option, &cur);
> >+              }
> >+      }
> >+      if (crash_base) {
> >+              mem_avoid[MEM_AVOID_CRASHKERNEL].start = crash_base;
> >+              mem_avoid[MEM_AVOID_CRASHKERNEL].size = crash_size;
> >+      } else {
> >+              /*
> >+               * Clearing mem_avoid if no offset is given. This is consistent
> >+               * with kernel, which uses the last crashkernel= option.
> >+               */
> >+              mem_avoid[MEM_AVOID_CRASHKERNEL].start = 0;
> >+              mem_avoid[MEM_AVOID_CRASHKERNEL].size = 0;
> >+      }
> >+}
> >
> > static void handle_mem_options(void)
> > {
> >@@ -248,7 +358,7 @@ 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);
> >@@ -284,6 +394,8 @@ static void handle_mem_options(void)
> >                               goto out;
> >
> >                       mem_limit = mem_size;
> >+              } else if (strstr(param, "crashkernel")) {
> >+                      mem_avoid_specified_crashkernel_region(val);
> >               }
> >       }
> >
> >@@ -412,7 +524,7 @@ 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();
> >
> >       /* Enumerate the immovable memory regions */
> >--
> >2.7.4
> >
> >
> >
>
>