On 30/05/2015 12:59, Xiao Guangrong wrote:
> Currently guest MTRR is completely prohibited if cache snoop is supported on
> IOMMU (!noncoherent_dma) and host does the emulation based on the knowledge
> from host side, however, host side is not the good point to know
> what the purpose of guest is. A good example is that pass-throughed VGA
> frame buffer is not always UC as host expected
Can you explain how? The original idea was that such a framebuffer
would be kvm_is_reserved_pfn and thus be unconditionally UC.
> +bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn,
> + int page_num)
> +{
> + struct mtrr_looker looker;
> + struct kvm_mtrr *mtrr_state = &vcpu->arch.mtrr_state;
> + u64 start = gfn_to_gpa(gfn), end = gfn_to_gpa(gfn + page_num);
> + int type = -1;
> +
> + mtrr_for_each_mem_type(&looker, mtrr_state, start, end) {
> + if (type == -1) {
> + type = looker.mem_type;
> + continue;
> + }
> +
> + if (type != looker.mem_type)
> + return false;
> + }
> +
> + if ((type != -1) && looker.partial_map &&
> + (mtrr_state->def_type != type))
> + return false;
> +
No Pascal-like parentheses.
Does this have a performance impact on shadow? Perhaps we could cache
in struct kvm_arch_memory_slot whether the memslot is covered by MTRRs?
Paolo
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