Messages in this thread | | | Date | Thu, 23 Dec 2021 18:26:06 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v18 02/17] x86/setup: Move xen_pv_domain() check and insert_resource() to setup_arch() |
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On Wed, Dec 22, 2021 at 09:08:05PM +0800, Zhen Lei wrote: > From: Chen Zhou <chenzhou10@huawei.com> > > We will make the functions reserve_crashkernel() as generic, the > xen_pv_domain() check in reserve_crashkernel() is relevant only to > x86,
Why is that so? Is Xen-PV x86-only?
> the same as insert_resource() in reserve_crashkernel[_low]().
Why?
Looking at
0212f9159694 ("x86: Add Crash kernel low reservation")
it *surprisingly* explains why that resources thing is being added:
We need to add another range in /proc/iomem like "Crash kernel low", so kexec-tools could find that info and append to kdump kernel command line.
Then,
157752d84f5d ("kexec: use Crash kernel for Crash kernel low")
renamed it because, as it states, kexec-tools was taught to handle multiple resources of the same name.
So why does kexec-tools on arm *not* need those iomem resources? How does it parse the ranges there? Questions over questions...
So last time I told you to sit down and take your time with this cleanup. From reading this here, it doesn't look like it. Rather, it looks like hastily done in a hurry and hurrying stuff doesn't help you one bit - it actually makes it worse.
Your commit messages need to explain *why* a change is being done and why is that ok. This one doesn't.
> @@ -1120,7 +1109,17 @@ void __init setup_arch(char **cmdline_p) > * Reserve memory for crash kernel after SRAT is parsed so that it > * won't consume hotpluggable memory. > */ > - reserve_crashkernel(); > +#ifdef CONFIG_KEXEC_CORE > + if (xen_pv_domain()) > + pr_info("Ignoring crashkernel for a Xen PV domain\n");
This is wrong - the check is currently being done inside reserve_crashkernel(), *after* it has parsed a crashkernel= cmdline correctly - and not before.
Your change would print on Xen PV, regardless of whether it has received crashkernel= on the cmdline or not.
This is exactly why I say that making those functions generic and shared might not be such a good idea, after all, because then you'd have to sprinkle around arch-specific stuff.
One of the ways how to address this particular case here would be:
1. Add a x86-specific wrapper around parse_crashkernel() which does all the parsing. When that wrapper finishes, you should have parsed everything that has crashkernel= on the cmdline.
2. At the end of that wrapper, you do arch-specific checks and setup like the xen_pv_domain() one.
3. Now, you do reserve_crashkernel(), if those checks pass.
The question is, whether the flow on arm64 can do the same. Probably but it needs careful auditing.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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