From: james.morse@arm•com (James Morse)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v2 11/11] arm64: kernel: Add support for hibernate/suspend-to-disk.
Date: Mon, 16 Nov 2015 14:01:04 +0000 [thread overview]
Message-ID: <5649E1A0.7020001@arm.com> (raw)
In-Reply-To: <20151116124116.GC9125@amd>
Hi,
On 16/11/15 12:41, Pavel Machek wrote:
>> On 14/11/15 21:34, Pavel Machek wrote:
>>>> The implementation assumes that exactly the same kernel is booted on the
>>>> same hardware, and that the kernel is loaded at the same physical address.
>>>
>>> BTW... on newer implementations (and I have patch for x86, too), we
>>> try to make it so that resume kernel does not have to be same as
>>> suspend one. It would be nice to move there with arm64, too.
>>
>> Yes, that is a neat trick, can I leave it as future work?
>
> Yes. But it is really not hard.
I think its harder than it looks:
It means the MMU has to be turned off, as two different kernels may not
have used the same configuration for the MMU - and I don't think its safe
to change while the MMU is running. There are also going to be
complications with resetting the hypervisor/el2 configuration, which I need
to spend more time thinking about (and probably ask for advice!).
>>>> + * Because this code has to be copied to a safe_page, it can't call out to
>>>> + * other functions by pc-relative address. Also remember that it
>>>
>>> PC-relative?
>>
>> The linker may (often!) use program-counter relative addresses for loads
>> and stores. This code gets copied, so the linker doesn't know where the
>> code will be executed from, so any instructions using pc-relative addresses
>> will get the wrong result, (if they reference something outside the
>> function).
>
> I was wondering if it should be spelled "PC-relative", not
> "pc-relative" :-).
Hah - sorry!
Fixed.
>>>> + * and executable pages mapped to user space are also written as data, we
>>>> + * clean all pages we touch to the PoU.
>>>
>>> What is PoC and PoU?
>>
>> They are points in the CPU's cache hierarchy:
>>
>> ARM processors are of a 'modified Harvard' architecture, their paths to
>> read instructions and data are different. The 'Point of Unification' is the
>> first point in the cache hierarchy that is the same for both. On ARM,
>> flush_icache_range() makes sure code written as data is pushed through any
>> data caches to this point, and then evicts any stale copies in the
>> instruction caches.
>>
>> PoC is the 'Point of Coherency', it is the first point that is the same for
>> all devices, (e.g. a cpu with caches turned on, and one with them off), it
>> is normally main memory. The kernel text has to be pushed to this point, so
>> that secondary cores, while running early-boot code with their MMU and
>> caches turned off, don't get incorrect code/data from before resume.
>>
>> I have resisted the urge to draw some ascii-art!
>
> That's ok, you just might want to replace PoI -> 'Point of
> Unification' and PoC -> 'Point of Coherency' in the comments. That
> should make googling easier for people not familiar with arm
> terminology.
There aren't any other points under arch/arm64 that use the full expansion,
but it can't hurt to include both.
Thanks,
James
next prev parent reply other threads:[~2015-11-16 14:01 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-27 17:29 [PATCH v2 00/11] arm64: kernel: Add support for hibernate/suspend-to-disk James Morse
2015-10-27 17:29 ` [PATCH v2 01/11] arm64: kernel: fix tcr_el1.t0sz restore on systems with extended idmap James Morse
2015-10-27 17:29 ` [PATCH v2 02/11] arm64: Fold proc-macros.S into assembler.h James Morse
2015-11-14 21:25 ` Pavel Machek
2015-11-16 18:44 ` Geoff Levand
2015-10-27 17:29 ` [PATCH v2 03/11] arm64: Convert hcalls to use HVC immediate value James Morse
2015-10-27 17:29 ` [PATCH v2 04/11] arm64: Add new hcall HVC_CALL_FUNC James Morse
2015-10-27 17:29 ` [PATCH v2 05/11] arm64: kvm: allows kvm cpu hotplug James Morse
2015-10-27 17:29 ` [PATCH v2 06/11] arm64: kernel: Rework finisher callback out of __cpu_suspend_enter() James Morse
2015-10-27 17:29 ` [PATCH v2 07/11] arm64: Change cpu_resume() to enable mmu early then access sleep_sp by va James Morse
2015-10-27 17:29 ` [PATCH v2 08/11] arm64: kernel: Include _AC definition in page.h James Morse
2015-10-27 17:29 ` [PATCH v2 09/11] arm64: Promote KERNEL_START/KERNEL_END definitions to a header file James Morse
2015-10-27 17:29 ` [PATCH v2 10/11] PM / Hibernate: clean cached pages on architectures that require it James Morse
2015-11-11 11:40 ` Lorenzo Pieralisi
2015-11-12 0:48 ` Rafael J. Wysocki
2015-11-12 11:47 ` Lorenzo Pieralisi
2015-11-13 23:38 ` Rafael J. Wysocki
2015-11-17 12:38 ` Lorenzo Pieralisi
2015-11-17 13:13 ` Pavel Machek
2015-11-17 13:43 ` Lorenzo Pieralisi
2015-11-12 2:53 ` Chen, Yu C
2015-11-12 11:52 ` Lorenzo Pieralisi
2015-11-14 20:26 ` Pavel Machek
2015-11-16 12:27 ` James Morse
2015-11-16 12:36 ` Pavel Machek
2015-11-26 14:23 ` James Morse
2015-10-27 17:29 ` [PATCH v2 11/11] arm64: kernel: Add support for hibernate/suspend-to-disk James Morse
2015-11-14 21:34 ` Pavel Machek
2015-11-16 12:29 ` James Morse
2015-11-16 12:41 ` Pavel Machek
2015-11-16 14:01 ` James Morse [this message]
2015-11-16 14:23 ` Mark Rutland
2015-11-16 18:01 ` Pavel Machek
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