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Message-ID: <a14bda4a-15ad-4d20-8b60-0ab92b608f2f@intel.com>
Date: Fri, 23 Feb 2024 11:39:07 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
x86@...nel.org
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
Elena Reshetova <elena.reshetova@...el.com>,
Jun Nakajima <jun.nakajima@...el.com>,
Rick Edgecombe <rick.p.edgecombe@...el.com>,
Tom Lendacky <thomas.lendacky@....com>, "Kalra, Ashish"
<ashish.kalra@....com>, Sean Christopherson <seanjc@...gle.com>,
"Huang, Kai" <kai.huang@...el.com>, Baoquan He <bhe@...hat.com>,
kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: Re: [PATCHv7 10/16] x86/tdx: Convert shared memory back to private on
kexec
On 2/12/24 02:44, Kirill A. Shutemov wrote:
> +static void tdx_kexec_stop_conversion(bool crash)
> +{
> + /* Stop new private<->shared conversions */
> + conversion_allowed = false;
> +
> + /*
> + * Make sure conversion_allowed is cleared before checking
> + * conversions_in_progress.
> + */
> + barrier();
> +
> + /*
> + * Crash kernel reaches here with interrupts disabled: can't wait for
> + * conversions to finish.
> + *
> + * If race happened, just report and proceed.
> + */
> + if (!crash) {
> + unsigned long timeout;
> +
> + /*
> + * Wait for in-flight conversions to complete.
> + *
> + * Do not wait more than 30 seconds.
> + */
> + timeout = 30 * USEC_PER_SEC;
> + while (atomic_read(&conversions_in_progress) && timeout--)
> + udelay(1);
> + }
> +
> + if (atomic_read(&conversions_in_progress))
> + pr_warn("Failed to finish shared<->private conversions\n");
> +}
I'd really prefer we find a way to do this with actual locks, especially
'conversion_allowed'.
This is _awfully_ close to being able to be handled by a rwsem where the
readers are the converters and tdx_kexec_stop_conversion() takes a write.
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