On Wed, May 11, 2022, Uros Bizjak wrote: > On Wed, May 11, 2022 at 9:54 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > Still, does 32bit actually support that stuff? > > Unfortunately, it does: > > kvm-intel-y += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \ > vmx/evmcs.o vmx/nested.o vmx/posted_intr.o > > And when existing cmpxchg64 is substituted with cmpxchg, the > compilation dies for 32bits with: ... > > Anyway, your patch looks about right, but I find it *really* hard to > > care about 32bit code these days. > > Thanks, this is also my sentiment, but I hope the patch will enable > better code and perhaps ease similar situation I have had elsewhere. IMO, if we merge this it should be solely on the benefits to 64-bit code. Yes, KVM still supports 32-bit kernels, but I'm fairly certain the only people that run 32-bit KVM are KVM developers. 32-bit KVM has been completely broken for multiple releases at least once, maybe twice, and no one ever complained. 32-bit KVM is mostly useful for testing the mess that is nested NPT; an L1 hypervsior can use 32-bit paging for NPT, so KVM needs to at least make sure it doesn't blow up if such a hypervisor is encountered. But in terms of the performance of 32-bit KVM, I doubt there is a person in the world that cares.
