Re: [PATCH v5 untested] kvm: better MWAIT emulation for guests

Gabriel L. Somlo
2017-03-16T16:52:32Z

On Thu, Mar 16, 2017 at 06:45:02PM +0200, Michael S. Tsirkin wrote:
> On Thu, Mar 16, 2017 at 12:16:13PM -0400, Gabriel L. Somlo wrote:
> > On Thu, Mar 16, 2017 at 04:35:18PM +0100, Radim Krčmář wrote:
> > > 2017-03-16 10:58-0400, Gabriel L. Somlo:
> > > > On Thu, Mar 16, 2017 at 04:04:12PM +0200, Michael S. Tsirkin wrote:
> > > > > On Thu, Mar 16, 2017 at 09:24:27AM -0400, Gabriel L. Somlo wrote:
> > > > > > After studying your patch a bit more carefully (sorry, it's crazy
> > > > > > around here right now :) ) I realized you're simply trying to
> > > > > > (selectively) decide when to exit L1 and emulate as NOP vs. when to
> > > > > > just allow L1 to execute MONITOR & MWAIT natively.
> > > > > >
> > > > > > Is that right ? Because if so, the issues I saw on my MacPro1,1 are
> > > > > > weird and inexplicable, given that allowing L>=1 to run MONITOR/MWAIT
> > > > > > natively was one of the options Alex Graf and Rene Rebe used back in
> > > > > > the very early days of OS X on QEMU, at the time I got involved with
> > > > > > that project. Here's part of an out of tree patch against 3.4 which did
> > > > > > just that, and worked as far as I remember on *any* MWAIT capable
> > > > > > intel chip I had access to back in 2010:
> > > > > >
> > > > > > ##############################################################################
> > > > > > # 99-mwait.patch.kvm-kmod (Rene Rebe <rene@exactcode.de>) 2010-04-27
> > > > > > ##############################################################################
> > > > > > diff -pNarU5 linux-3.4/arch/x86/kvm/cpuid.c linux-3.4-mac/arch/x86/kvm/cpuid.c
> > > > > > --- linux-3.4/arch/x86/kvm/cpuid.c 2012-05-20 18:29:13.000000000 -0400
> > > > > > +++ linux-3.4-mac/arch/x86/kvm/cpuid.c 2012-10-09 11:42:59.921215750 -0400
> > > > > > @@ -222,11 +222,11 @@ static int do_cpuid_ent(struct kvm_cpuid
> > > > > > f_nx | 0 /* Reserved */ | F(MMXEXT) | F(MMX) |
> > > > > > F(FXSR) | F(FXSR_OPT) | f_gbpages | f_rdtscp |
> > > > > > 0 /* Reserved */ | f_lm | F(3DNOWEXT) | F(3DNOW);
> > > > > > /* cpuid 1.ecx */
> > > > > > const u32 kvm_supported_word4_x86_features =
> > > > > > - F(XMM3) | F(PCLMULQDQ) | 0 /* DTES64, MONITOR */ |
> > > > > > + F(XMM3) | F(PCLMULQDQ) | F(MWAIT) /* DTES64, MONITOR */ |
> > > > > > 0 /* DS-CPL, VMX, SMX, EST */ |
> > > > > > 0 /* TM2 */ | F(SSSE3) | 0 /* CNXT-ID */ | 0 /* Reserved */ |
> > > > > > F(FMA) | F(CX16) | 0 /* xTPR Update, PDCM */ |
> > > > > > 0 /* Reserved, DCA */ | F(XMM4_1) |
> > > > > > F(XMM4_2) | F(X2APIC) | F(MOVBE) | F(POPCNT) |
> > > > > > diff -pNarU5 linux-3.4/arch/x86/kvm/svm.c linux-3.4-mac/arch/x86/kvm/svm.c
> > > > > > --- linux-3.4/arch/x86/kvm/svm.c 2012-05-20 18:29:13.000000000 -0400
> > > > > > +++ linux-3.4-mac/arch/x86/kvm/svm.c 2012-10-09 11:44:41.598997481 -0400
> > > > > > @@ -1102,12 +1102,10 @@ static void init_vmcb(struct vcpu_svm *s
> > > > > > set_intercept(svm, INTERCEPT_VMSAVE);
> > > > > > set_intercept(svm, INTERCEPT_STGI);
> > > > > > set_intercept(svm, INTERCEPT_CLGI);
> > > > > > set_intercept(svm, INTERCEPT_SKINIT);
> > > > > > set_intercept(svm, INTERCEPT_WBINVD);
> > > > > > - set_intercept(svm, INTERCEPT_MONITOR);
> > > > > > - set_intercept(svm, INTERCEPT_MWAIT);
> > > > > > set_intercept(svm, INTERCEPT_XSETBV);
> > > > > >
> > > > > > control->iopm_base_pa = iopm_base;
> > > > > > control->msrpm_base_pa = __pa(svm->msrpm);
> > > > > > control->int_ctl = V_INTR_MASKING_MASK;
> > > > > > diff -pNarU5 linux-3.4/arch/x86/kvm/vmx.c linux-3.4-mac/arch/x86/kvm/vmx.c
> > > > > > --- linux-3.4/arch/x86/kvm/vmx.c 2012-05-20 18:29:13.000000000 -0400
> > > > > > +++ linux-3.4-mac/arch/x86/kvm/vmx.c 2012-10-09 11:42:59.925215977 -0400
> > > > > > @@ -1938,11 +1938,11 @@ static __init void nested_vmx_setup_ctls
> > > > > > nested_vmx_procbased_ctls_low, nested_vmx_procbased_ctls_high);
> > > > > > nested_vmx_procbased_ctls_low = 0;
> > > > > > nested_vmx_procbased_ctls_high &=
> > > > > > CPU_BASED_VIRTUAL_INTR_PENDING | CPU_BASED_USE_TSC_OFFSETING |
> > > > > > CPU_BASED_HLT_EXITING | CPU_BASED_INVLPG_EXITING |
> > > > > > - CPU_BASED_MWAIT_EXITING | CPU_BASED_CR3_LOAD_EXITING |
> > > > > > + CPU_BASED_CR3_LOAD_EXITING |
> > > > > > CPU_BASED_CR3_STORE_EXITING |
> > > > > > #ifdef CONFIG_X86_64
> > > > > > CPU_BASED_CR8_LOAD_EXITING | CPU_BASED_CR8_STORE_EXITING |
> > > > > > #endif
> > > > > > CPU_BASED_MOV_DR_EXITING | CPU_BASED_UNCOND_IO_EXITING |
> > > > > > @@ -2404,12 +2404,10 @@ static __init int setup_vmcs_config(stru
> > > > > > CPU_BASED_CR3_LOAD_EXITING |
> > > > > > CPU_BASED_CR3_STORE_EXITING |
> > > > > > CPU_BASED_USE_IO_BITMAPS |
> > > > > > CPU_BASED_MOV_DR_EXITING |
> > > > > > CPU_BASED_USE_TSC_OFFSETING |
> > > > > > - CPU_BASED_MWAIT_EXITING |
> > > > > > - CPU_BASED_MONITOR_EXITING |
> > > > > > CPU_BASED_INVLPG_EXITING |
> > > > > > CPU_BASED_RDPMC_EXITING;
> > > > > >
> > > > > > opt = CPU_BASED_TPR_SHADOW |
> > > > > > CPU_BASED_USE_MSR_BITMAPS |
> > > > > >
> > > > > > If all you're trying to do is (selectively) revert to this behavior,
> > > > > > that "shouldn't" mess it up for the MacPro either, so I'm thoroughly
> > > > > > confused at this point :)
> > > > >
> > > > > Yes. Me too. Want to try that other patch and see what happens?
> > > >
> > > > You mean the old 3.4 patch against current KVM ? I'll try to do that,
> > > > might take me a while :)
> > >
> > > Michael's patch already did most of that, you just need to add
> > >
> > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > > index efde6cc50875..b12f07d4ce17 100644
> > > --- a/arch/x86/kvm/cpuid.c
> > > +++ b/arch/x86/kvm/cpuid.c
> > > @@ -348,7 +348,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> > > const u32 kvm_cpuid_1_ecx_x86_features =
> > > /* NOTE: MONITOR (and MWAIT) are emulated as NOP,
> > > * but *not* advertised to guests via CPUID ! */
> > > - F(XMM3) | F(PCLMULQDQ) | 0 /* DTES64, MONITOR */ |
> > > + F(XMM3) | F(PCLMULQDQ) | F(MWAIT) /* DTES64, MONITOR */ |
> > > 0 /* DS-CPL, VMX, SMX, EST */ |
> > > 0 /* TM2 */ | F(SSSE3) | 0 /* CNXT-ID */ | 0 /* Reserved */ |
> > > F(FMA) | F(CX16) | 0 /* xTPR Update, PDCM */ |
> > >
> > > Note: this will never be upstream, because mwait isn't what we want by
> > > default. :)
> >
> > But since OS X doesn't check CPUID and simply runs MONITOR & MWAIT
> > assuming they're present, the above one-liner would make no
> > difference. If everything else in the old patch I quoted is identical
> > to what Michael does, then I don't know -- maybe the MacPro1,1 has
> > really broken L>=1 MWAIT, and it only ever worked with vmexit and
> > emulation on the host side.
>
>
> I think I have an idea. It is probably one of the monitor bugs
> on this host.
>
> X86_BUG_CLFLUSH_MONITOR or X86_BUG_MONITOR.
>
> If you tell guest you have a CPU that does not need it
> but host does need it, then mwait will not work.
>
> if (c->x86 == 6 && boot_cpu_has(X86_FEATURE_CLFLUSH) &&
> (c->x86_model == 29 || c->x86_model == 46 || c->x86_model == 47))
> set_cpu_bug(c, X86_BUG_CLFLUSH_MONITOR);
>
>
> if (c->x86 == 6 && boot_cpu_has(X86_FEATURE_MWAIT) &&
> ((c->x86_model == INTEL_FAM6_ATOM_GOLDMONT)))
> set_cpu_bug(c, X86_BUG_MONITOR);
>
> what did you say your host model is?

# dmidecode -t1
# dmidecode 2.12
SMBIOS 2.4 present.

Handle 0x0021, DMI type 1, 27 bytes
System Information
Manufacturer: Apple Computer, Inc.
Product Name: MacPro1,1
Version: 1.0
Serial Number: G87030UEUPZ
UUID: 9CFE245E-D0C8-BD45-A79F-54EA5FBD3D97
Wake-up Type: Power Switch
SKU Number: System SKU#
Family: MacPro

Thx,
--G