Le 19/06/2018 à 21:50, Jaromir Dolecek a écrit :
Module Name: src
Committed By: jdolecek
Date: Tue Jun 19 19:50:19 UTC 2018
Modified Files:
src/sys/arch/x86/include: fpu.h
src/sys/arch/x86/x86: cpu.c fpu.c identcpu.c
src/sys/arch/xen/x86: cpu.c
Log Message:
fix FPU initialization on Xen to allow e.g. AVX when supported by hardware;
only use XSAVE when the the CPUID OSXSAVE bit is set, as this seems to be
reliable indication
tested with Xen 4.2.6 DOM0/DOMU on Intel CPU, without and with no-xsave flag,
so should work also on those AMD CPUs, which have XSAVE disabled by default;
also tested with Xen DOM0 4.8.3
fixes PR kern/50332 by Torbjorn Granlund; sorry it took three years to address
XXX pullup netbsd-8
I don't understand, and it looks wrong.
-- fxsave
fpuinit_mxcsr_mask calls fxsave, not xsave. The availability of fxsave is
controlled by CR4_OSFXSR, not CR4_OSXSAVE. It seems to me that the check you
added in fpuinit_mxcsr_mask is wrong, because it is confusing fxsave and
xsave.
[x86_fpu_save = FPU_SAVE_FXSAVE] guarantees fxsave is supported.
fpuinit_mxcsr_mask is called only when this condition is true, so there is no
need for a check in the first place.
The reason I disabled the code on Xen, if I remember correctly, was because
of a stack alignment problem. For some reason this variable
union savefpu fpusave __aligned(16);
was not always 16-byte aligned on Xen. So fxsave would fault.
-- xsave
Please keep the initialization logic consistent.
xen/x86/cpu.c
554 if (cpu_feature[1] & CPUID2_OSXSAVE)
555 cr4 |= CR4_OSXSAVE;
556 else {
557 x86_xsave_features = 0;
558 x86_fpu_save = FPU_SAVE_FXSAVE;
559 }
If the availability of xsave on xen is determined by CPUID2_OSXSAVE (as
opposed to CPUID2_XSAVE on native), then put the code in identcpu.c just
like native.
That is to say
x86/x86/identcpu.c
804 /* See if xsave (for AVX) is supported */
805 if ((ci->ci_feat_val[1] & CPUID2_XSAVE) == 0)
806 return;
XXX
XXX #ifdef XEN
XXX /* On Xen we also need to check CPUID2_OSXSAVE */
XXX if ((ci->ci_feat_val[1] & CPUID2_OSXSAVE) == 0)
XXX return;
XXX #endif
Note also that your change seems wrong on i386 too, because you enable fxsave
if we don't have xsave, while we may have neither.
