Re: [PATCH v7 43/45] virt: Add SEV-SNP guest driver

From: Randy Dunlap <rdunlap@infradead.org>
To: Brijesh Singh <brijesh.singh@amd.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, linux-efi@vger.kernel.org,
	platform-driver-x86@vger.kernel.org, linux-coco@lists.linux.dev,
	linux-mm@kvack.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Jim Mattson <jmattson@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	Dov Murik <dovmurik@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@ibm.com>,
	Borislav Petkov <bp@alien8.de>,
	Michael Roth <michael.roth@amd.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	Andi Kleen <ak@linux.intel.com>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
	tony.luck@intel.com, marcorr@google.com,
	sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH v7 43/45] virt: Add SEV-SNP guest driver
Date: Thu, 11 Nov 2021 14:57:59 -0800	[thread overview]
Message-ID: <e6b412e4-f38e-d212-f52a-e7bdc9a26eff@infradead.org> (raw)
In-Reply-To: <38e5047c-43a9-400b-c507-337011e0e605@amd.com>

On 11/11/21 11:27 AM, Brijesh Singh wrote:
> Hi Randy,
> 
> On 11/10/21 4:27 PM, Randy Dunlap wrote:
>> Hi,
>>
>> On 11/10/21 2:07 PM, Brijesh Singh wrote:
>>> diff --git a/drivers/virt/coco/sevguest/Kconfig b/drivers/virt/coco/sevguest/Kconfig
>>> new file mode 100644
>>> index 000000000000..96190919cca8
>>> --- /dev/null
>>> +++ b/drivers/virt/coco/sevguest/Kconfig
>>> @@ -0,0 +1,9 @@
>>> +config SEV_GUEST
>>> +    tristate "AMD SEV Guest driver"
>>> +    default y
>>
>> For this to remain as "default y", you need to justify it.
>> E.g., if a board cannot boot with an interrupt controller,
>> the driver for the interrupt controller can be "default y".
>>
>> So why is this default y?
>> No other drivers in drivers/virt/ are default y.
>>
> 
> I choose the default "y" for two reasons:
> 
> 1.  The driver is built if the user enables the AMD memory encryption support. If the user has selected the AMD memory encryption support, they will be querying an attestation report to verify that the guest is running on AMD memory encryption enabled hardware.

OK, I see. I'm OK with this.

> 2. Typically, an attestation report is retrieved from an initial ramdisk (before mounting the disk). IIUC, the standard initramfs build tools may not include the driver by default and requires the user to go through hoops.
> 
> However, I have no strong reason to keep it to "y" if other prefers "m".

"m" is no better than "y" in this case.

thanks.
-- 
~Randy