From: Bhupesh Sharma <bhsharma@redhat.com>
To: James Morse <james.morse@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
ard.biesheuvel@linaro.org, catalin.marinas@arm.com,
kexec@lists.infradead.org, Will Deacon <will.deacon@arm.com>,
AKASHI Takahiro <takahiro.akashi@linaro.org>,
bhupesh.linux@gmail.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64, vmcoreinfo : Append 'MAX_USER_VA_BITS' and 'MAX_PHYSMEM_BITS' to vmcoreinfo
Date: Mon, 4 Feb 2019 20:05:41 +0530 [thread overview]
Message-ID: <a646e38d-9351-e187-1571-c49d3558b164@redhat.com> (raw)
In-Reply-To: <86c0dd9f-a55b-8ce8-69ca-893f63087d1a@redhat.com>
Hi James, All,
On 01/31/2019 03:09 AM, Bhupesh Sharma wrote:
> Hi James,
>
> Thanks for review.
> Please see my comments inline.
>
>
> On 01/30/2019 08:51 PM, James Morse wrote:
>> Hi Bhupesh,
>>
>> On 01/30/2019 12:23 PM, Bhupesh Sharma wrote:
>>> With ARMv8.2-LVA and LPA architecture extensions, arm64 hardware which
>>> supports these extensions can support upto 52-bit virtual and 52-bit
>>> physical addresses respectively.
>>>
>>> Since at the moment we enable the support of these extensions via CONFIG
>>> flags, e.g.
>>> - LPA via CONFIG_ARM64_PA_BITS_52
>>>
>>> there are no clear mechanisms in user-space right now to
>>> deteremine these CONFIG flag values and also determine the PARange and
>>> VARange address values.
>>> User-space tools like 'makedumpfile' and 'crash-utility' can instead
>>> use the 'MAX_USER_VA_BITS' and 'MAX_PHYSMEM_BITS' values to determine
>>> the maximum virtual address and physical address (respectively)
>>> supported by underlying kernel.
>>>
>>> A reference 'makedumpfile' implementation which uses this approach to
>>> determining the maximum physical address is available in [0].
>>
>> Why does it need to know?
>>
>> (Suzuki asked the same question on your earlier version)
>> https://lore.kernel.org/linux-arm-kernel/cff44754-7fe4-efea-bc8e-4dde2277c821@arm.com/
>
>
> I have shared some details (after discussion with our test teams) in
> reply to the review comments from Suzuki here:
> http://lists.infradead.org/pipermail/kexec/2019-January/022389.html, and
> http://lists.infradead.org/pipermail/kexec/2019-January/022390.html
>
> Just to summarize, I mentioned in my replies to the review comments tha
> the makedumpfile implementation (for decoding the PTE) was just as an
> example, however there can be other user-space applications, for e.g a
> user-space application running with 48-bit kernel VA and 52-bit user
> space VA and requesting allocation in 'high' address via a 'hint' to mmap.
>
>> From your github link it looks like you use this to re-assemble the
>> two bits of the PFN from the pte. Can't you always do this for 64K
>> pages? CPUs with the feature always do this too, its not something the
>> kernel turns on.
>
> Ok, let me try to give some perspective of a common makedumpfile
> use-case before I jump into the details:
>
> (a) makedumpfile tool can be used to generate a vmcore and analyze it
> later. So for example we can create vmcore for a system running with
> page-size = 64K and analyze it later on a different system using
> page-size = 4K.
>
> Since several makedumpfile code legs (for page-table walk) are common in
> both the paths (creating a vmcore and analyzing a vmcore), we cannot
> hardcode the PTE calculation masks for either 48-bit or 52-bit address
> spaces (or 4K/64K page sizes). The example invocations for the two cases
> is given below:
>
> Create a vmcore dump on a 64K machine:
> # makedumpfile -l --message-level 1 -d 31 /proc/vmcore vmcore
>
> Analyze the vmcore dump on a 4K machine:
> # makedumpfile -d 31 -x vmlinux vmcore dumpfile
>
> Also hardcoding the PTE calculation to use the high address bit mask
> always will break the backward compatibility with older kernels (which
> don't support 52-bit address space extensions).
>
> (b). Also x86_64 already has a vmcoreinfo export for 'pgtable_l5_enabled':
>
> void arch_crash_save_vmcoreinfo(void)
> {
> <.. snip..>
> vmcoreinfo_append_str("NUMBER(pgtable_l5_enabled)=%d\n",
> pgtable_l5_enabled());
> }
>
> And the makedumpfile code uses the same to determine support for 5-level
> page tables in x86_64, see
> <https://github.com/bhupesh-sharma/makedumpfile/blob/52-bit-pa-support-via-vmcore-v1/arch/x86_64.c#L36>
> for example.
Ping. Since this patch fixes a regression with user-space tools like
makedumpfile and crash-utility which are broken since arm64 kernels
with 52-bit VA and PA support are available (and distributions which
enable them), would request review comments/ack on this simple change.
Thanks,
Bhupesh
>>
>>> diff --git a/arch/arm64/kernel/crash_core.c
>>> b/arch/arm64/kernel/crash_core.c
>>> index ca4c3e12d8c5..ad231be5c0d8 100644
>>> --- a/arch/arm64/kernel/crash_core.c
>>> +++ b/arch/arm64/kernel/crash_core.c
>>> @@ -10,6 +10,8 @@
>>> void arch_crash_save_vmcoreinfo(void)
>>> {
>>> VMCOREINFO_NUMBER(VA_BITS);
>>> + VMCOREINFO_NUMBER(MAX_USER_VA_BITS);
>>> + VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
>>> /* Please note VMCOREINFO_NUMBER() uses "%d", not "%x" */
>>> vmcoreinfo_append_str("NUMBER(kimage_voffset)=0x%llx\n",
>>> kimage_voffset);
>>>
>>
>
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next prev parent reply other threads:[~2019-02-04 14:35 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-30 12:23 [PATCH] arm64, vmcoreinfo : Append 'MAX_USER_VA_BITS' and 'MAX_PHYSMEM_BITS' to vmcoreinfo Bhupesh Sharma
2019-01-30 15:21 ` James Morse
2019-01-30 21:39 ` Bhupesh Sharma
2019-02-04 14:35 ` Bhupesh Sharma [this message]
2019-02-04 15:31 ` Robin Murphy
2019-02-12 4:55 ` Bhupesh Sharma
2019-02-12 10:49 ` Robin Murphy
2019-02-04 16:56 ` James Morse
2019-01-31 1:48 ` Dave Young
2019-01-31 10:00 ` Bhupesh Sharma
2019-01-31 14:03 ` Dave Anderson
2019-02-04 16:04 ` Kazuhito Hagio
2019-02-12 5:07 ` Bhupesh Sharma
2019-02-12 10:44 ` Dave Young
2019-02-12 19:59 ` Bhupesh Sharma
2019-02-12 23:03 ` Kazuhito Hagio
2019-02-13 11:15 ` Dave Young
2019-02-13 18:22 ` James Morse
2019-02-13 19:52 ` Kazuhito Hagio
2019-02-15 17:34 ` James Morse
2019-02-15 18:01 ` Bhupesh Sharma
2019-02-18 15:27 ` Steve Capper
2019-02-21 16:08 ` Bhupesh Sharma
2019-02-19 20:47 ` Kazuhito Hagio
2019-02-21 16:20 ` Bhupesh Sharma
2019-02-21 16:42 ` Dave Anderson
2019-02-21 19:02 ` Kazuhito Hagio
2019-03-01 4:01 ` Bhupesh Sharma
2019-02-14 19:30 ` Bhupesh Sharma
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