linux-kernel - Re: [PATCH v3 2/2] x86/sev: Add support to unaccept memory after hot-remove

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Message-ID: <097a4980-9d10-40d2-9667-d07bf19e7b86@amd.com>
Date: Thu, 29 Jan 2026 11:32:37 -0600
From: "Pratik R. Sampat" <prsampat@....com>
To: Kiryl Shutsemau <kas@...nel.org>, Dave Hansen <dave.hansen@...el.com>
Cc: linux-mm@...ck.org, linux-coco@...ts.linux.dev, x86@...nel.org,
 linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
 bp@...en8.de, dave.hansen@...ux.intel.com, ardb@...nel.org,
 akpm@...ux-foundation.org, david@...nel.org, osalvador@...e.de,
 thomas.lendacky@....com, michael.roth@....com
Subject: Re: [PATCH v3 2/2] x86/sev: Add support to unaccept memory after
 hot-remove

On 1/29/26 4:40 AM, Kiryl Shutsemau wrote:
> On Wed, Jan 28, 2026 at 01:15:06PM -0800, Dave Hansen wrote:
>> On 1/28/26 12:41, Pratik R. Sampat wrote:
>>> +static inline void arch_unaccept_memory(phys_addr_t start, phys_addr_t end)
>>> +{
>>> +	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP)) {
>>> +		snp_unaccept_memory(start, end);
>>> +	} else {
>>> +		panic("Cannot unaccept memory: unknown platform\n");
>>> +	}
>>> +}
>>
>> This panic() is pretty nasty.
>>
>> Can't we just disable memory hotplug up front if it's:
>>
>> 	!cc_platform_has(CC_ATTR_GUEST_SEV_SNP)
>>
>> ?
> 
> I don't understand SEV-SNP situation, but I don't think we need to do
> anything on unplug for TDX. We should expect the unplugged memory to be
> removed from SEPT. If VMM doesn't do this, it is effectively DoS and we
> don't protect against DoS in CoCo.
> 
> Converting the memory to shared will do no good for us.

In that case a fall through for TDX (with a comment explaining why) and
panic for rest may be the way to go?

>