Re: [PATCH v1 11/26] x86/sev: Invalidate pages from the direct map when adding them to the RMP table

Vlastimil Babka
2024-01-12T20:27:49Z

On 1/12/24 21:07, Borislav Petkov wrote:
> On Fri, Jan 12, 2024 at 12:00:01PM -0800, Dave Hansen wrote:
>> On 12/30/23 08:19, Michael Roth wrote:
>> > If the kernel uses a 2MB directmap mapping to write to an address, and
>> > that 2MB range happens to contain a 4KB page that set to private in the
>> > RMP table, that will also lead to a page-fault exception.
>>
>> I thought we agreed long ago to just demote the whole direct map to 4k
>> on kernels that might need to act as SEV-SNP hosts. That should be step
>> one and this can be discussed as an optimization later.
>
> What would be the disadvantage here? Higher TLB pressure when running
> kernel code I guess...

Yeah and last LSF/MM we concluded that it's not as a big disadvantage as we
previously thought https://lwn.net/Articles/931406/