On Mon, Jun 03, 2019 at 06:56:17PM +0200, Radim Krčmář wrote: > > + break; > > + } > > entry->eax = min(entry->eax, (u32)(f_intel_pt ? 0x14 : 0xd)); > > Similarly in the existing code. If we don't have f_intel_pt, then we > should make sure that leaf 0x14 is not being filled, but we don't really > have to limit the maximal index. > > Adding a single clamping like > > /* Limited to the highest leaf implemented in KVM. */ > entry->eax = min(entry->eax, 0x1f); > > seems sufficient. > > (Passing the hardware value is ok in theory, but it is a cheap way to > avoid future leaves that cannot be simply zeroed for some weird reason.) I don't have a strong opinion regarding the code itself, but whatever ends up getting committed should have a big beefy changelog explaining why the clamping exists, or at least extolling its virtues. I had a hell of a time understanding the intent of this one line of code because as your response shows, there is no one right answer.
