From: Dave Hansen <redacted> Sent: Thursday, February 23, 2023 12:42 PM

On 2/23/23 12:26, Dave Hansen wrote:

quoted

quoted

+       if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
+               /*
+               * Ensure fixmaps for IOAPIC MMIO respect memory encryption pgprot
+               * bits, just like normal ioremap():
+               */
+               if (x86_platform.hyper.is_private_mmio(phys))
+                       flags = pgprot_encrypted(flags);
+               else
+                       flags = pgprot_decrypted(flags);
+       }

...

quoted

It does seem a bit odd that there's a new CC_ATTR_GUEST_MEM_ENCRYPT
check wrapping this whole thing.  I guess the trip through
pgprot_decrypted() is harmless on normal platforms, though.

Yeah, that's _really_ odd.  Sean, were you trying to optimize away the
indirect call or something?

I would just expect the Hyper-V/vTOM code to leave
x86_platform.hyper.is_private_mmio alone unless
it *knows* the platform has private MMIO *and* CC_ATTR_GUEST_MEM_ENCRYPT.

Agreed.

Is there ever a case where CC_ATTR_GUEST_MEM_ENCRYPT==0 and he
Hyper-V/vTOM code would need to set x86_platform.hyper.is_private_mmio?

There's no such case. 

I agree that gating with CC_ATTR_GUEST_MEM_ENCRYPT isn't really necessary.
Current upstream code always does the pgprot_decrypted(), and as you said,
that's a no-op on platforms with no memory encryption.

Michael