Il 20/08/2014 15:58, Nadav Amit ha scritto: > IA32_MISC_ENABLE MSR has two bits that affect the actual results which can be > observed by the guest: fast string enable, and FOPCODE compatibility. Guests > may wish to change the default settings of these bits. > > Linux usually enables fast-string by default. However, when "fast string" is > enabled data breakpoints are only recognized on boundaries between data-groups. > On some old CPUs enabling fast-string also resulted in single-step not > occurring upon each iteration. > > FOPCODE compatibility can be used to analyze program performance by recording > the last instruction executed before FSAVE/FSTENV/FXSAVE. > > This patch saves and restores these bits in IA32_MISC_ENABLE if they are > supported upon entry to guest and exit to userspace respectively. To avoid > possible issues, fast-string can only be enabled by the guest if the host > enabled them. The physical CPU version is checked to ensure no shared bits are > reconfigured in the process. Maybe I'm dense :) but why are you saying upon exit to userspace? It is switched upon VM exit simply. In fact I was thinking you'd use kvm_set_shared_msr for this, but it looks like you aren't doing that. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
