Messages in this thread | | | Subject | Re: [RFC 00/16] KVM protected memory extension | From | Liran Alon <> | Date | Tue, 26 May 2020 13:16:14 +0300 |
| |
On 26/05/2020 9:17, Mike Rapoport wrote: > On Mon, May 25, 2020 at 04:47:18PM +0300, Liran Alon wrote: >> On 22/05/2020 15:51, Kirill A. Shutemov wrote: >> >> Furthermore, I would like to point out that just unmapping guest data from >> kernel direct-map is not sufficient to prevent all >> guest-to-guest info-leaks via a kernel memory info-leak vulnerability. This >> is because host kernel VA space have other regions >> which contains guest sensitive data. For example, KVM per-vCPU struct (which >> holds vCPU state) is allocated on slab and therefore >> still leakable. > Objects allocated from slab use the direct map, vmalloc() is another story. It doesn't matter. This patch series, like XPFO, only removes guest memory pages from direct-map. Not things such as KVM per-vCPU structs. That's why Julian & Marius (AWS), created the "Process local kernel VA region" patch-series that declare a single PGD entry, which maps a kernelspace region, to have different PFN between different tasks. For more information, see my KVM Forum talk slides I gave in previous reply and related AWS patch-series: https://patchwork.kernel.org/cover/10990403/ > >>> - Touching direct mapping leads to fragmentation. We need to be able to >>> recover from it. I have a buggy patch that aims at recovering 2M/1G page. >>> It has to be fixed and tested properly >> As I've mentioned above, not mapping all guest memory from 1GB hugetlbfs >> will lead to holes in kernel direct-map which force it to not be mapped >> anymore as a series of 1GB huge-pages. >> This have non-trivial performance cost. Thus, I am not sure addressing this >> use-case is valuable. > Out of curiosity, do we actually have some numbers for the "non-trivial > performance cost"? For instance for KVM usecase? > Dig into XPFO mailing-list discussions to find out... I just remember that this was one of the main concerns regarding XPFO.
-Liran
| |