linux-kernel - Re: [PATCHv11 11/19] x86/tdx: Convert shared memory back to private on kexec

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Date: Tue, 4 Jun 2024 09:27:59 -0700
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>, Ard Biesheuvel <ardb@...nel.org>,
 Baoquan He <bhe@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
 "K. Y. Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, kexec@...ts.infradead.org,
 linux-hyperv@...r.kernel.org, linux-acpi@...r.kernel.org,
 linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Tao Liu <ltao@...hat.com>
Subject: Re: [PATCHv11 11/19] x86/tdx: Convert shared memory back to private
 on kexec

On 5/28/24 02:55, Kirill A. Shutemov wrote:
> +/* Stop new private<->shared conversions */
> +static void tdx_kexec_begin(bool crash)
> +{
> +	/*
> +	 * Crash kernel reaches here with interrupts disabled: can't wait for
> +	 * conversions to finish.
> +	 *
> +	 * If race happened, just report and proceed.
> +	 */
> +	if (!set_memory_enc_stop_conversion(!crash))
> +		pr_warn("Failed to stop shared<->private conversions\n");
> +}

I don't like having to pass 'crash' in here.

If interrupts are the problem we have ways of testing for those directly.

If it's being in an oops that's a problem, we have 'oops_in_progress'
for that.

In other words, I'd much rather this function (or better yet
set_memory_enc_stop_conversion() itself) use some existing API to change
its behavior in a crash rather than have the context be passed down and
twiddled through several levels of function calls.

There are a ton of these in the console code:

	if (oops_in_progress)
		foo_trylock();
	else
		foo_lock();

To me, that's a billion times more clear than a 'wait' argument that
gets derives from who-knows-what that I have to trace through ten levels
of function calls.