[PATCH 1/9] x86/kexec: Disable global pages before writing to control page

[Dave Hansen]

On 12/17/24 04:25, Kirill A. Shutemov wrote:
>> Clear the PGE bit in %cr4 early, before storing data in the control page.
> It worth noting that flipping CR4.PGE triggers TLB flush. I was not sure
> if CR3 write is required to make it happen.

I thought about removing the CR3 write. But I decided against it because
CR4.PGE needs to actually change value, unlike CR3 writes where any
write can flush the TLB (modulo globals, PCID and bit 63 of course).

X86_FEATURE_PGE itself is required but I couldn't actually remember if
there are any cases where CR4.PGE==0. If there were, the CR3 write would
still be needed. I don't _think_ there are any ways forx86_64 to end up
with CR4.PGE==0, but I also wouldn't out the possibility that some silly
issue pops up making us play stupid games and win stupid prizes.

Anyway, I think we can leave the belt-and-suspenders programming in this
case. A comment wouldn't hurt I guess.