On 8/27/21 10:18 AM, Borislav Petkov wrote: > On Fri, Aug 20, 2021 at 10:19:27AM -0500, Brijesh Singh wrote: >> From: Michael Roth <michael.roth@xxxxxxx> >> >> This adds support for utilizing the SEV-SNP-validated CPUID table in > s/This adds support for utilizing/Utilize/ > > Yap, it can really be that simple. :) > >> the various #VC handler routines used throughout boot/run-time. Mostly >> this is handled by re-using the CPUID lookup code introduced earlier >> for the boot/compressed kernel, but at various stages of boot some work >> needs to be done to ensure the CPUID table is set up and remains >> accessible throughout. The following init routines are introduced to >> handle this: > Do not talk about what your patch does - that should hopefully be > visible in the diff itself. Rather, talk about *why* you're doing what > you're doing. > >> sev_snp_cpuid_init(): > This one is not really introduced - it is already there. > > <snip all the complex rest> > > So this patch is making my head spin. It seems we're dancing a lot of > dance just to have our CPUID page present at all times. Which begs the > question: do we need it during the whole lifetime of the guest? Mike can correct me, we need it for entire lifetime of the guest. Whenever guest needs the CPUID value, the #VC handler will refer to this page. > Regardless, I think this can be simplified by orders of > magnitude if we allocated statically 4K for that CPUID page in > arch/x86/boot/compressed/mem_encrypt.S, copied the supplied CPUID page > from the firmware to it and from now on, work with our own copy. Actually a VMM could populate more than one page for the CPUID. One page can include 64 entries and I believe Mike is already running into limits (with Qemu) and exploring the ideas to extend it more than a page. > You probably would need to still remap it for kernel proper but it would > get rid of all that crazy in this patch here. > > Hmmm? >
