On 17/10/2018 19:08, Jim Mattson wrote: > I believe that ESXi reads GUEST_CS_AR_BYTES on every VM-exit to > determine code size.
Which makes me wonder, maybe we should add GUEST_SS_AR_BYTES which is where the CPL lives. But then your tests from last year didn't find it. Paolo > On Wed, Oct 17, 2018 at 10:02 AM, Paolo Bonzini <[email protected]> wrote: >> On 17/10/2018 16:47, Vitaly Kuznetsov wrote: >>>>> + if (!hv_evmcs || !(hv_evmcs->hv_clean_fields & >>>>> + HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP2)) { >>>>> + vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector); >>>>> + vmcs_write32(GUEST_CS_LIMIT, vmcs12->guest_cs_limit); >>>>> + vmcs_write32(GUEST_CS_AR_BYTES, vmcs12->guest_cs_ar_bytes); >>>>> + vmcs_writel(GUEST_ES_BASE, vmcs12->guest_es_base); >>>>> + vmcs_writel(GUEST_CS_BASE, vmcs12->guest_cs_base); >>>>> + } >>>> For what it's worth, I suspect that these can be moved to >>>> prepare_vmcs02_full. The initial implementation of shadow VMCS did not >>>> expose "unrestricted guest" to the L1 hypervisor, and emulation does a >>>> lot of accesses to CS (of course). Not sure how ES base ended up in >>>> there and not DS base, though... >>> I tried unshadowing all these fields and at least Hyper-V on KVM >>> (without using eVMCS of course) experiences a 1200-1300 cpu cycles >>> regression during tight cpuid loop test. I checked and this happens >>> because it likes vmreading GUEST_CS_AR_BYTES a lot. >> >> Go figure. :) Liran, do you happen to know if ESX does something >> similar with CS descriptor cache fields? >> >> Paolo
