From: lijiang <lijiang@redhat.com>
To: Dave Young <dyoung@redhat.com>,
"Eric W. Biederman" <ebiederm@xmission.com>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org,
bhe@redhat.com, jgross@suse.com, dhowells@redhat.com,
Thomas.Lendacky@amd.com, vgoyal@redhat.com,
kexec@lists.infradead.org
Subject: Re: [PATCH 3/3 v3] x86/kdump: clean up all the code related to the backup region
Date: Mon, 14 Oct 2019 18:02:22 +0800 [thread overview]
Message-ID: <f3fc12b9-be39-d430-52f5-d1b76b2599a3@redhat.com> (raw)
In-Reply-To: <20191012121625.GA11587@dhcp-128-65.nay.redhat.com>
在 2019年10月12日 20:16, Dave Young 写道:
> Hi Eric,
>
> On 10/12/19 at 06:26am, Eric W. Biederman wrote:
>> Lianbo Jiang <lijiang@redhat.com> writes:
>>
>>> When the crashkernel kernel command line option is specified, the
>>> low 1MiB memory will always be reserved, which makes that the memory
>>> allocated later won't fall into the low 1MiB area, thereby, it's not
>>> necessary to create a backup region and also no need to copy the first
>>> 640k content to a backup region.
>>>
>>> Currently, the code related to the backup region can be safely removed,
>>> so lets clean up.
>>>
>>> Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
>>> ---
>>
>>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>>> index eb651fbde92a..cc5774fc84c0 100644
>>> --- a/arch/x86/kernel/crash.c
>>> +++ b/arch/x86/kernel/crash.c
>>> @@ -173,8 +173,6 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
>>>
>>> #ifdef CONFIG_KEXEC_FILE
>>>
>>> -static unsigned long crash_zero_bytes;
>>> -
>>> static int get_nr_ram_ranges_callback(struct resource *res, void *arg)
>>> {
>>> unsigned int *nr_ranges = arg;
>>> @@ -234,9 +232,15 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
>>> {
>>> struct crash_mem *cmem = arg;
>>>
>>> - cmem->ranges[cmem->nr_ranges].start = res->start;
>>> - cmem->ranges[cmem->nr_ranges].end = res->end;
>>> - cmem->nr_ranges++;
>>> + if (res->start >= SZ_1M) {
>>> + cmem->ranges[cmem->nr_ranges].start = res->start;
>>> + cmem->ranges[cmem->nr_ranges].end = res->end;
>>> + cmem->nr_ranges++;
>>> + } else if (res->end > SZ_1M) {
>>> + cmem->ranges[cmem->nr_ranges].start = SZ_1M;
>>> + cmem->ranges[cmem->nr_ranges].end = res->end;
>>> + cmem->nr_ranges++;
>>> + }
>>
>> What is going on with this chunk? I can guess but this needs a clear
>> comment.
>
> Indeed it needs some code comment, this is based on some offline
> discussion. cat /proc/vmcore will give a warning because ioremap is
> mapping the system ram.
>
> We pass the first 1M to kdump kernel in e820 as system ram so that 2nd
> kernel can use the low 1M memory because for example the trampoline
> code.
>
Thank you, Eric and Dave. I will add the code comment as below if it would be OK.
@@ -234,9 +232,20 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
{
struct crash_mem *cmem = arg;
- cmem->ranges[cmem->nr_ranges].start = res->start;
- cmem->ranges[cmem->nr_ranges].end = res->end;
- cmem->nr_ranges++;
+ /*
+ * Currently, pass the low 1MiB range to kdump kernel in e820
+ * as system ram so that kdump kernel can also use the low 1MiB
+ * memory due to the real mode trampoline code.
+ * And later, the low 1MiB range will be exclued from elf header,
+ * which will avoid remapping the 1MiB system ram when dumping
+ * vmcore.
+ */
+ if (res->start >= SZ_1M) {
+ cmem->ranges[cmem->nr_ranges].start = res->start;
+ cmem->ranges[cmem->nr_ranges].end = res->end;
+ cmem->nr_ranges++;
+ } else if (res->end > SZ_1M) {
+ cmem->ranges[cmem->nr_ranges].start = SZ_1M;
+ cmem->ranges[cmem->nr_ranges].end = res->end;
+ cmem->nr_ranges++;
+ }
return 0;
}
>>
>>>
>>> return 0;
>>> }
>>
>>> @@ -356,9 +337,12 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
>>> memset(&cmd, 0, sizeof(struct crash_memmap_data));
>>> cmd.params = params;
>>>
>>> - /* Add first 640K segment */
>>> - ei.addr = image->arch.backup_src_start;
>>> - ei.size = image->arch.backup_src_sz;
>>> + /*
>>> + * Add the low memory range[0x1000, SZ_1M], skip
>>> + * the first zero page.
>>> + */
>>> + ei.addr = PAGE_SIZE;
>>> + ei.size = SZ_1M - PAGE_SIZE;
>>> ei.type = E820_TYPE_RAM;
>>> add_e820_entry(params, &ei);
>>
>> Likewise here. Why do we need a special case?
>> Why the magic with PAGE_SIZE?
>
> Good catch, the zero page part is useless, I think no other special
> reason, just assumed zero page is not usable, but it should be ok to
> remove the special handling, just pass 0 - 1M is good enough.
>> Thanks
> Dave
>
next prev parent reply other threads:[~2019-10-14 10:02 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-12 2:21 [PATCH 0/3 v3] x86/kdump: Fix 'kmem -s' reported an invalid freepointer when SME was active Lianbo Jiang
2019-10-12 2:21 ` [PATCH 1/3 " Lianbo Jiang
2019-10-12 2:21 ` [PATCH 2/3 v3] x86/kdump cleanup: remove the unused crash_copy_backup_region() Lianbo Jiang
2019-10-12 2:21 ` [PATCH 3/3 v3] x86/kdump: clean up all the code related to the backup region Lianbo Jiang
2019-10-12 11:26 ` Eric W. Biederman
2019-10-12 12:16 ` Dave Young
2019-10-13 3:54 ` Eric W. Biederman
2019-10-13 9:36 ` lijiang
2019-10-15 11:04 ` Eric W. Biederman
2019-10-16 8:40 ` lijiang
2019-10-16 14:30 ` lijiang
2019-10-16 16:51 ` Eric W. Biederman
2019-10-13 10:20 ` Dave Young
2019-10-14 10:02 ` lijiang [this message]
2019-10-15 11:11 ` Eric W. Biederman
2019-10-16 3:24 ` lijiang
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