Messages in this thread | | | Subject | Re: [PATCH v8 4/5] x86/xsave: Make XSAVE check the base CPUID features before enabling | From | Vegard Nossum <> | Date | Sat, 29 Jun 2019 17:22:59 +0200 |
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On 10/5/17 11:52 PM, Andi Kleen wrote: > From: Andi Kleen <ak@linux.intel.com> > > Before enabling XSAVE, not only check the XSAVE specific CPUID bits, > but also the base CPUID features of the respective XSAVE feature. > This allows to disable individual XSAVE states using the existing > clearcpuid= option, which can be useful for performance testing > and debugging, and also in general avoids inconsistencies. > > v2: > Add curly brackets (Thomas Gleixner) > Signed-off-by: Andi Kleen <ak@linux.intel.com> > --- > arch/x86/kernel/fpu/xstate.c | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c > index f1d5476c9022..924bd895b5ee 100644 > --- a/arch/x86/kernel/fpu/xstate.c > +++ b/arch/x86/kernel/fpu/xstate.c > @@ -15,6 +15,7 @@ > #include <asm/fpu/xstate.h> > > #include <asm/tlbflush.h> > +#include <asm/cpufeature.h> > > /* > * Although we spell it out in here, the Processor Trace > @@ -36,6 +37,19 @@ static const char *xfeature_names[] = > "unknown xstate feature" , > }; > > +static short xsave_cpuid_features[] = { > + X86_FEATURE_FPU, > + X86_FEATURE_XMM, > + X86_FEATURE_AVX, > + X86_FEATURE_MPX, > + X86_FEATURE_MPX, > + X86_FEATURE_AVX512F, > + X86_FEATURE_AVX512F, > + X86_FEATURE_AVX512F, > + X86_FEATURE_INTEL_PT, > + X86_FEATURE_PKU, > +}; > + > /* > * Mask of xstate features supported by the CPU and the kernel: > */ > @@ -726,6 +740,7 @@ void __init fpu__init_system_xstate(void) > unsigned int eax, ebx, ecx, edx; > static int on_boot_cpu __initdata = 1; > int err; > + int i; > > WARN_ON_FPU(!on_boot_cpu); > on_boot_cpu = 0; > @@ -759,6 +774,14 @@ void __init fpu__init_system_xstate(void) > goto out_disable; > } > > + /* > + * Clear XSAVE features that are disabled in the normal CPUID. > + */ > + for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) { > + if (!boot_cpu_has(xsave_cpuid_features[i])) > + xfeatures_mask &= ~BIT(i); > + } > + > xfeatures_mask &= fpu__get_supported_xfeatures_mask(); > > /* Enable xstate instructions to be able to continue with initialization: */ >
Hi,
The commit for this patch in mainline (ccb18db2ab9d923df07e7495123fe5fb02329713) causes the kernel to hang on boot when passing the "nofxsr" option:
$ kvm -cpu host -kernel arch/x86/boot/bzImage -append "console=ttyS0 nofxsr earlyprintk=ttyS0" -serial stdio -display none -smp 2 early console in extract_kernel input_data: 0x0000000001dea276 input_len: 0x0000000000500704 output: 0x0000000001000000 output_len: 0x00000000012c79b4 kernel_total_size: 0x0000000000f24000 booted via startup_32() Physical KASLR using RDRAND RDTSC... Virtual KASLR using RDRAND RDTSC...
Decompressing Linux... Parsing ELF... Performing relocations... done. Booting the kernel. [..hang..]
If I revert it from Linus's tree (~5.2-rc6) then it boots again:
early console in extract_kernel input_data: 0x00000000024192e9 input_len: 0x00000000005d8ea1 output: 0x0000000001000000 output_len: 0x00000000019c7fa4 kernel_total_size: 0x000000000162c000 trampoline_32bit: 0x000000000009d000 booted via startup_32() Physical KASLR using RDRAND RDTSC... Virtual KASLR using RDRAND RDTSC...
Decompressing Linux... Parsing ELF... Performing relocations... done. Booting the kernel. Linux version 5.2.0-rc6+ (vegard@t460) (gcc version 5.5.0 20171010 (Ubuntu 5.5.0-12ubuntu1~16.04)) #98 SMP PREEMPT Sat Jun 29 17:13:31 CEST 2019 Command line: console=ttyS0 nofxsr earlyprintk=ttyS0 [..normal boot..]
/proc/cpuinfo inside the VM is:
processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 78 model name : Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz stepping : 3 microcode : 0x1 cpu MHz : 2496.000 cache size : 4096 KB physical id : 0 siblings : 1 core id : 0 cpu cores : 1 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon rep_good nopl cpuid tsc_known_freq pni pclmulqdq vmx ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch cpuid_fault invpcid_single pti ssbd ibrs ibpb tpr_shadow vnmi flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm mpx rdseed adx smap clflushopt xsaveopt xsavec xgetbv1 xsaves arat bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds bogomips : 4992.00 clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management:
Vegard
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