Re: [PATCH v6 00/12] SVM cleanup and INVPCID feature support

On 24/03/21 22:21, Borislav Petkov wrote:

 	if (kaiser_enabled)
  		invpcid_flush_one(X86_CR3_PCID_ASID_USER, addr);
+	else
+		asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
+
  	invpcid_flush_one(X86_CR3_PCID_ASID_KERN, addr);
  }

I think the kernel ASID flush can also be moved under the "if"?

and the reason why it does, IMHO, is because on AMD, kaiser_enabled is
false because AMD is not affected by Meltdown, which means, there's no
user/kernel pagetables split.

And that also means, you have global TLB entries which means that if you
look at that __native_flush_tlb_single() function, it needs to flush
global TLB entries on CPUs with X86_FEATURE_INVPCID_SINGLE by doing an
INVLPG in the kaiser_enabled=0 case. Errgo, the above hunk.

Makes sense.

Paolo