Re: [PATCH v3 1/8] x86/sev: Prepare for using the RMPREAD instruction to access the RMP

[Nikunj A. Dadhania]

On 10/16/2024 8:13 PM, Tom Lendacky wrote:
> On 10/16/24 03:52, Nikunj A. Dadhania wrote:
>> On 9/30/2024 8:52 PM, Tom Lendacky wrote:
>>> The RMPREAD instruction returns an architecture defined format of an
>>> RMP entry. This is the preferred method for examining RMP entries.
>>>
 
>>> +static int __snp_lookup_rmpentry(u64 pfn, struct rmpentry *entry, int *level)
>>> +{
>>> +	struct rmpentry large_entry;
>>> +	int ret;
>>> +
>>> +	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
>>> +		return -ENODEV;
>>
>> Can we rely on rmp_table check in __get_rmpentry() and remove the above check ?
>> If rmp_table is NULL, CC_ATTR_HOST_SEV_SNP is always cleared.
> 
> I'm trying to not change the logic and just add the new struct usage.
> Once RMPREAD is used there is no checking of the table address and if
> SNP is not enabled in the SYSCFG MSR the instruction will #UD.

Sure, makes sense.
 
> The table address check is just to ensure we don't accidentally call
> this function without checking CC_ATTR_HOST_SEV_SNP in the future to
> avoid a possible crash. If anything, I can remove the table address
> check that I added here, but I would like to keep it just to be safe.

Regards
Nikunj