Re: [PATCH v6 9/9] x86: Pass memory range via E820 for kdump

Dave Young
2014-04-17T06:43:22Z

On 04/17/14 at 02:32pm, Dave Young wrote:
> On 04/17/14 at 02:17pm, WANG Chao wrote:
> > On 04/17/14 at 01:35pm, Dave Young wrote:
> > > On 04/17/14 at 01:29pm, Dave Young wrote:
> > > > On 04/14/14 at 10:55pm, WANG Chao wrote:
> > > > > command line size is restricted by kernel, sometimes memmap=exactmap has
> > > > > too many memory ranges to pass to cmdline. And also memmap=exactmap and
> > > > > kASLR doesn't work together.
> > > > >
> > > > > A better approach, to pass the memory ranges for crash kernel to boot
> > > > > into, is filling the memory ranges into E820.
> > > > >
> > > > > boot_params only got 128 slots for E820 map to fit in, when the number of
> > > > > memory map exceeds 128, use setup_data to pass the rest as extended E820
> > > > > memory map.
> > > > >
> > > > > kexec boot could also benefit from setup_data in case E820 memory map
> > > > > exceeds 128.
> > > > >
> > > > > Now this new approach becomes default instead of memmap=exactmap.
> > > > > saved_max_pfn users can specify --pass-memmap-cmdline to use the
> > > > > exactmap approach.
> > > > >
> > > > > Signed-off-by: WANG Chao <chaowang@redhat.com>
> > > > > Tested-by: Linn Crosetto <linn@hp.com>
> > > > > Reviewed-by: Linn Crosetto <linn@hp.com>
> > > > > ---
> > > > > kexec/arch/i386/crashdump-x86.c | 6 +-
> > > > > kexec/arch/i386/x86-linux-setup.c | 149 +++++++++++++++++++++++++-------------
> > > > > kexec/arch/i386/x86-linux-setup.h | 1 +
> > > > > 3 files changed, 103 insertions(+), 53 deletions(-)
> > > > >
> > > > > diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
> > > > > index 7b618a6..4a1491b 100644
> > > > > --- a/kexec/arch/i386/crashdump-x86.c
> > > > > +++ b/kexec/arch/i386/crashdump-x86.c
> > > > > @@ -979,7 +979,8 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline,
> > > > > dbgprintf("Created elf header segment at 0x%lx\n", elfcorehdr);
> > > > > if (delete_memmap(memmap_p, &nr_memmap, elfcorehdr, memsz) < 0)
> > > > > return -1;
> > > > > - cmdline_add_memmap(mod_cmdline, memmap_p);
> > > > > + if (arch_options.pass_memmap_cmdline)
> > > > > + cmdline_add_memmap(mod_cmdline, memmap_p);
> > > > > if (!bzImage_support_efi_boot)
> > > > > cmdline_add_efi(mod_cmdline);
> > > > > cmdline_add_elfcorehdr(mod_cmdline, elfcorehdr);
> > > > > @@ -995,7 +996,8 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline,
> > > > > type = mem_range[i].type;
> > > > > size = end - start + 1;
> > > > > add_memmap(memmap_p, &nr_memmap, start, size, type);
> > > > > - cmdline_add_memmap_acpi(mod_cmdline, start, end);
> > > > > + if (arch_options.pass_memmap_cmdline)
> > > > > + cmdline_add_memmap_acpi(mod_cmdline, start, end);
> > > >
> > > > Seems memmap_p contains the acpi ranges as well, so cmdline_add_memmap_acpi is
> > > > not necessary anymore, just improve cmdline_add_memmap to add both RAM and ACPI
> > > > ranges is enough.
> > >
> > > CRASH_MAX_MEMMAP_NR is used in cmdline_add_memmap, it does not include the acpi
> > > ranges, it looks strange, but anyway there's checking about cmdline overflow, tos
> > > I think maybe this CRASH_MAX_MEMMAP_NR can be dropped.
> >
> > First, naming cmdline_add_memmap is not accurate regarding what the
> > function does (adding RAM only). But it's historical naming issue,
> > nothing to do with this patch :(
> >
> > I'm sure that could be improved later.
> >
> > Second, about dropping CRASH_MAX_MEMMAP_NR, I'm not sure if it's a good
> > idea.
> >
> > CRASH_MAX_MEMMAP_NR is used to allocate memmap_p memory:
> >
> > load_crash_segments(){
> > [..]
> > sz = (sizeof(struct memory_range) * CRASH_MAX_MEMMAP_NR);
> > memmap_p = xmalloc(sz);
> > memset(memmap_p, 0, sz);
> > [..]
> > }
> >
> > And so that every time when we walk through memmap_p,
> > CRASH_MAX_MEMMAP_NR can be used as a upper boundary.
> >
> > I think maintain CRASH_MAX_MEMMAP_NR is reasonable and necessary based
> > on the current code base.
>
> Hmm, if it's used for allocate mem range array then how about directly use
> CRASH_MAX_MEMORY_RANGES which is same in your 5/9.

I really would like to see a cleaner code, but since this issue is trival
I will not object it now.

For the calgary issue I'm curious if there are people who report a bug.
At least if that happens we will know that there's actually someone who
are using the calgary code.

Thanks
Dave