Messages in this thread | | | Date | Mon, 13 Jul 2015 22:45:06 +0800 | From | Xiao Guangrong <> | Subject | Re: [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR |
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On 07/13/2015 03:32 PM, Paolo Bonzini wrote:
>>> I'm seeing a significant regression in boot performance on Intel >>> hardware with assigned devices that bisects back to this patch. There's >>> a long delay with Seabios between the version splash and execution of >>> option ROMs, and a _very_ long delay with OVMF before the display is >>> initialized. The delay is long enough that users are reporting their >>> previously working VM is hung with 100% CPU usage on v4.2-rc1. Thanks, >>> >> >> Alex, thanks for your report. I will try to reproduce and fix it asap. >
I have reproduced the issue and I think Bandan and Paolo is correct.
> The code that Bandan pointed out > > + /* MTRR is completely disabled, use UC for all of physical memory. */ > + if (!(mtrr_state->enabled & 0x2)) > + return MTRR_TYPE_UNCACHABLE; > > actually disappears in commit fa61213746a7 (KVM: MTRR: simplify > kvm_mtrr_get_guest_memory_type, 2015-06-15). Should mtrr_default_type > actually be something like this:
:(
Based on the SDM, UC is applied to all memory rather than default-type if MTRR is disabled.
If i changed the code to: if (!(mtrr_state->enabled & 0x2)) return mtrr_state->def_type; the result is the same as before.
However, fast boot came back if "return 0xFF" here. So fast boot expects that the memory type is WB.
> > static u8 mtrr_default_type(struct kvm_mtrr *mtrr_state) > { > if (mtrr_is_enabled(mtrr_state)) > return mtrr_state->deftype & IA32_MTRR_DEF_TYPE_TYPE_MASK; > else > return MTRR_TYPE_UNCACHABLE; > } > > ? Then it's easy to add a quirk that makes the default WRITEBACK until > MTRRs are enabled.
It is the wrong configure in OVMF... shall we need to adjust KVM to satisfy OVMF?
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