On 6/5/2023 8:13 PM, Vitaly Kuznetsov wrote:
@@ -113,6 +114,11 @@ static int hv_cpu_init(unsigned int cpu)
}
if (!WARN_ON(!(*hvp))) {
+ if (hv_isolation_type_en_snp()) {
+ WARN_ON_ONCE(set_memory_decrypted((unsigned long)(*hvp), 1));
+ memset(*hvp, 0, PAGE_SIZE);
+ }
Why do we need to set the page as decrypted here and not when we
allocate the page (a few lines above)?
If Linux root partition boots in the SEV-SNP guest, the page still needs
to be decrypted.
And why do we need to clear it
_after_ we made it decrypted? In case we care about not leaking the
stale content to the hypervisor, we should've cleared it_before_, but
the bigger problem I see is that memset() is problemmatic e.g. for KVM
which uses enlightened VMCS. You put a CPU offline and then back online
and this path will be taken. Clearing VP assist page will likely brake
things. (AFAIU SEV-SNP Hyper-V guests don't expose SVM yet so the
problem is likely theoretical only, but still).
The page will be made dirt by hardware after decrypting operation and so
memset the page after that.
