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Date: Tue, 7 Dec 2010 10:01:48 +0800
From: Sheng Yang <sheng@...ux.intel.com>
To: Jeremy Fitzhardinge <jeremy@...p.org>
Cc: Stefano Stabellini <stefano.stabellini@...citrix.com>,
linux-kernel@...r.kernel.org,
"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH v2] xen: HVM X2APIC support
On Tuesday 07 December 2010 02:07:23 Jeremy Fitzhardinge wrote:
> On 12/05/2010 11:49 PM, Sheng Yang wrote:
> > This patch is similiar to Gleb Natapov's patch for KVM, which enable the
> > hypervisor to emulate x2apic feature for the guest. By this way, the
> > emulation of lapic would be simpler with x2apic interface(MSR), and
> > faster.
> >
> > Signed-off-by: Sheng Yang <sheng@...ux.intel.com>
> > ---
> >
> > arch/x86/include/asm/xen/hypervisor.h | 35
> > +++++++++++++++++++++++++++++++++ arch/x86/kernel/apic/apic.c
> > | 4 ++-
> > arch/x86/xen/enlighten.c | 30 ++++++++++-----------------
> > 3 files changed, 49 insertions(+), 20 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/xen/hypervisor.h
> > b/arch/x86/include/asm/xen/hypervisor.h index 396ff4c..bc5b804 100644
> > --- a/arch/x86/include/asm/xen/hypervisor.h
> > +++ b/arch/x86/include/asm/xen/hypervisor.h
> > @@ -37,4 +37,39 @@
> >
> > extern struct shared_info *HYPERVISOR_shared_info;
> > extern struct start_info *xen_start_info;
> >
> > +#include <asm/processor.h>
> > +
> > +static inline uint32_t xen_cpuid_base(void)
> > +{
> > + uint32_t base, eax, ebx, ecx, edx;
> > + char signature[13];
> > +
> > + for (base = 0x40000000; base < 0x40010000; base += 0x100) {
> > + cpuid(base, &eax, &ebx, &ecx, &edx);
> > + *(uint32_t *)(signature + 0) = ebx;
> > + *(uint32_t *)(signature + 4) = ecx;
> > + *(uint32_t *)(signature + 8) = edx;
> > + signature[12] = 0;
> > +
> > + if (!strcmp("XenVMMXenVMM", signature) && ((eax - base) >= 2))
> > + return base;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +#ifdef CONFIG_XEN
> > +extern bool xen_hvm_need_lapic(void);
> > +
> > +static inline bool xen_para_available(void)
> > +{
> > + return xen_hvm_need_lapic();
> > +}
> > +#else
> > +static inline bool xen_para_available(void)
> > +{
> > + return (xen_cpuid_base() != 0);
> > +}
> > +#endif
>
> Surely this should be using the asm/hypervisor.h interface?
I think it's the proper place. Or any suggestion?
>
> > +
> >
> > #endif /* _ASM_X86_XEN_HYPERVISOR_H */
> >
> > diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> > index 3f838d5..1b68221 100644
> > --- a/arch/x86/kernel/apic/apic.c
> > +++ b/arch/x86/kernel/apic/apic.c
> > @@ -52,6 +52,7 @@
> >
> > #include <asm/mce.h>
> > #include <asm/kvm_para.h>
> > #include <asm/tsc.h>
> >
> > +#include <asm/xen/hypervisor.h>
> >
> > unsigned int num_processors;
> >
> > @@ -1476,7 +1477,8 @@ void __init enable_IR_x2apic(void)
> >
> > /* IR is required if there is APIC ID > 255 even when running
> >
> > * under KVM
> > */
> >
> > - if (max_physical_apicid > 255 || !kvm_para_available())
> > + if (max_physical_apicid > 255 ||
> > + (!kvm_para_available() && !xen_para_available()))
> >
> > goto nox2apic;
>
> What are the downsides of just using x2apic unconditionally?
>
> Assuming there is some downside to using it all the time, what about
> adding a pseudo-cpu feature flag meaning "use x2apic unconditionally"
> rather than adding a bunch of ad-hoc tests here?
Because for native, x2apic should be used with interrupt-remapping, otherwise it
didn't make much sense for native(the main reason to x2apic for bare-metal is
support big machine with more than 255 APIC-ID, and without interrupt remapping it
can't do so). But for hypervisor, we want to emulate the accessing faster through
MSR, so we want them.
>
> > /*
> >
> > * without IR all CPUs can be addressed by IOAPIC/MSI
> >
> > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > index 235c0f4..7ef1645 100644
> > --- a/arch/x86/xen/enlighten.c
> > +++ b/arch/x86/xen/enlighten.c
> > @@ -1245,25 +1245,6 @@ asmlinkage void __init xen_start_kernel(void)
> >
> > #endif
> > }
> >
> > -static uint32_t xen_cpuid_base(void)
> > -{
> > - uint32_t base, eax, ebx, ecx, edx;
> > - char signature[13];
> > -
> > - for (base = 0x40000000; base < 0x40010000; base += 0x100) {
> > - cpuid(base, &eax, &ebx, &ecx, &edx);
> > - *(uint32_t *)(signature + 0) = ebx;
> > - *(uint32_t *)(signature + 4) = ecx;
> > - *(uint32_t *)(signature + 8) = edx;
> > - signature[12] = 0;
> > -
> > - if (!strcmp("XenVMMXenVMM", signature) && ((eax - base) >= 2))
> > - return base;
> > - }
> > -
> > - return 0;
> > -}
> > -
> >
> > static int init_hvm_pv_info(int *major, int *minor)
> > {
> >
> > uint32_t eax, ebx, ecx, edx, pages, msr, base;
> >
> > @@ -1373,6 +1354,17 @@ static bool __init xen_hvm_platform(void)
> >
> > return true;
> >
> > }
> >
> > +bool xen_hvm_need_lapic(void)
>
> Where does this get used?
?... xen_para_available() above...
--
regards
Yang, Sheng
>
> > +{
> > + if (xen_pv_domain())
> > + return false;
> > + if (xen_hvm_domain() &&
> > + (xen_feature(XENFEAT_hvm_pirqs) || xen_have_vector_callback))
> > + return false;
> > + return (xen_cpuid_base() != 0);
> > +}
> > +EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
> > +
> >
> > const __refconst struct hypervisor_x86 x86_hyper_xen_hvm = {
> >
> > .name = "Xen HVM",
> > .detect = xen_hvm_platform,
>
> J
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