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Message-ID: <noym2bqgxqcyhhdzoax7gvdfzhh7rtw7cv236fhzpqh3wqf76e@2jj733skv7y4>
Date: Tue, 4 Jun 2024 18:32:44 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: adrian.hunter@...el.com, ardb@...nel.org, ashish.kalra@....com,
bhe@...hat.com, dave.hansen@...ux.intel.com, elena.reshetova@...el.com,
haiyangz@...rosoft.com, hpa@...or.com, jun.nakajima@...el.com, kai.huang@...el.com,
kexec@...ts.infradead.org, kys@...rosoft.com, linux-acpi@...r.kernel.org,
linux-coco@...ts.linux.dev, linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
ltao@...hat.com, mingo@...hat.com, peterz@...radead.org, rafael@...nel.org,
rick.p.edgecombe@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com, seanjc@...gle.com,
tglx@...utronix.de, thomas.lendacky@....com, x86@...nel.org
Subject: Re: [PATCHv11.1 11/19] x86/tdx: Convert shared memory back to
private on kexec
On Mon, Jun 03, 2024 at 10:37:54AM +0200, Borislav Petkov wrote:
> On Sun, Jun 02, 2024 at 05:23:03PM +0300, Kirill A. Shutemov wrote:
> > + /*
> > + * The only thing one can do at this point on failure
> > + * is panic. It is reasonable to proceed.
>
> It makes even less sense now: panic() means "all stops and we die" and
> you say it is reasonable to proceed.
>
> I'm confused.
Right.
What about the comment below?
/*
* One possible reason for the failure is if kexec raced
* with memory conversion. In this case shared bit in
* page table got set (or not cleared) during
* shared<->private conversion, but the page is actually
* private. So this failure is not going to affect the
* kexec'ed kernel.
*
* The only thing one can do at this point on failure
* at this point is panic. In absence of better options,
* it is reasonable to proceed, hoping the failure is a
* benign shared bit mismatch due to the race.
*
* Also, even if the failure is real and the page cannot
* be touched as private, the kdump kernel will boot
* fine as it uses pre-reserved memory. What happens
* next depends on what the dumping process does and
* there's a reasonable chance to produce useful dump
* on crash.
*
* Regardless, the print leaves a trace in the log to
* give a clue for debug.
*/
--
Kiryl Shutsemau / Kirill A. Shutemov
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