linux-kernel - Re: [PATCH 1/1] x86/hyperv: Use Hyper-V entropy to seed guest random number generator

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Message-ID: <Zeuk3ixlvMFg1CDo@liuwe-devbox-debian-v2>
Date: Fri, 8 Mar 2024 23:53:02 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Michael Kelley <mhklinux@...look.com>
Cc: "wei.liu@...nel.org" <wei.liu@...nel.org>,
	"haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
	"decui@...rosoft.com" <decui@...rosoft.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"bp@...en8.de" <bp@...en8.de>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"hpa@...or.com" <hpa@...or.com>, "arnd@...db.de" <arnd@...db.de>,
	"tytso@....edu" <tytso@....edu>,
	"Jason@...c4.com" <Jason@...c4.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Saurabh Singh Sengar <ssengar@...rosoft.com>,
	Long Li <longli@...rosoft.com>
Subject: Re: [PATCH 1/1] x86/hyperv: Use Hyper-V entropy to seed guest random
 number generator

On Wed, Mar 06, 2024 at 05:43:41PM +0000, Michael Kelley wrote:
> From: wei.liu@...nel.org @ 2024-03-04  6:57 UTC
> > 
> > > +void __init ms_hyperv_late_init(void)
> > > +{
> > > +	struct acpi_table_header *header;
> > > +	acpi_status status;
> > > +	u8 *randomdata;
> > > +	u32 length, i;
> > > +
> > > +	/*
> > > +	 * Seed the Linux random number generator with entropy provided by
> > > +	 * the Hyper-V host in ACPI table OEM0.  It would be nice to do this
> > > +	 * even earlier in ms_hyperv_init_platform(), but the ACPI subsystem
> > > +	 * isn't set up at that point. Skip if booted via EFI as generic EFI
> > > +	 * code has already done some seeding using the EFI RNG protocol.
> > > +	 */
> > > +	if (!IS_ENABLED(CONFIG_ACPI) || efi_enabled(EFI_BOOT))
> > > +		return;
> > > +
> > > +	status = acpi_get_table("OEM0", 0, &header);
> > > +	if (ACPI_FAILURE(status) || !header) {
> > > +		pr_info("Hyper-V: ACPI table OEM0 not found\n");
> > 
> > I would like this to be a pr_debug() instead of pr_info(), considering
> > using the negative case may cause users to think not having this table
> > can be problematic.
> > 
> > Alternatively, we can remove this message here, and then ...
> > 
> > > +		return;
> > > +	}
> > > +
> > 
> > ... add a pr_debug() here to indicate that the table was found.
> > 
> > 	pr_info("Hyper-V: Seeding randomness with data from ACPI table OEM0\n");
> 
> You wrote the code as "pr_info()" but your comment suggests "pr_debug()".
> I'm assuming pr_debug() is better because we don't really need any output

Yes, I meant to use pr_debug() here. Sorry for the confusion. The
pr_info() was a c&p error.

Thanks,
Wei.