Bochs SVM:which processor support nRIP?

[akgupt3]

Hi all,
I see that Bochs SVM NRIP support is only for Generic (AMD?)processor.

anish-mac:bochs-2.6 akgupt3$ grep -nr SVM_NRIP cpu
cpu/cpuid.h:433:#define BX_CPUID_SVM_NRIP_SAVE (1 << 3)
cpu/generic_cpuid.cc:644: leaf->edx = BX_CPUID_SVM_NESTED_PAGING | BX_CPUID_SVM_NRIP_SAVE;
cpu/generic_cpuid.cc BX_CPUID_SVM_NRIP_SAVE;
cpu/svm.cc:582: if (BX_SUPPORT_SVM_EXTENSION(BX_CPUID_SVM_NRIP_SAVE))

PhenomX3 8650 doesn't support nRIP, I verified using FreeBSD and checked CPUID Fn8000_000A using a kernel module.

I am not sure how to specify to use Generic AMD core in bochsrc file, for Phenom, I specified model=phenom_8650_toliman but for Generic, I had it as vendor_string=AuthenticAMD but bochs didn't start, error us "cpu directive is malformed".

Looks like Phenom also doesn't support instruction decode(SVM CPUID capability), I wonder how can hypervisor increment RIP w/o nRIP and instruction decode.

[stlw]

Hi,

You could browse for various CPUIDs here:
http://instlatx64.atw.hu/

Yes, you cannot configure the nrip (or any other svm subfeature) using bx_generic cpuid.
Also the CPUID definition modules currently doesn't include CPUs which cannot be fully emulated by Bochs with all their bell and whistles - might be it is already time to change it.
I am aware of one AMD CPU which supported NRIP - it is Bulldozer.
Bochs doesn't support some of the Bulldozer features and therefore its CPUID definition wasn't added to CPUDB yet.
Might be I need to create smth like Bulldozer ES which will have subset of real Bulldozer which Bochs knows to emulate.

BTW, if you know to re-compile Bochs sources you could simply go to phenomx3_8650_toliman.cc file and add NRIP into it - you will receive phenom which does support NRIP.

Currently phenom has:

Code: Select all

Bit32u phenom_8650_toliman_t::get_svm_extensions_bitmask(void) const
{
  return BX_CPUID_SVM_NESTED_PAGING |
         BX_CPUID_SVM_LBR_VIRTUALIZATION |
         BX_CPUID_SVM_SVM_LOCK;
}

// leaf 0x8000000A : SVM //
void phenom_8650_toliman_t::get_ext_cpuid_leaf_A(cpuid_function_t *leaf) const
{
  leaf->eax = 0x01; /* SVM revision ID */
  leaf->ebx = 0x40; /* number of ASIDs */
  leaf->ecx = 0;

  // * [0:0]   NP - Nested paging support
  // * [1:1]   LBR virtualization
  // * [2:2]   SVM Lock
  //   [3:3]   NRIPS - Next RIP save on VMEXIT
  //   [4:4]   TscRate - MSR based TSC ratio control
  //   [5:5]   VMCB Clean bits support
  //   [6:6]   Flush by ASID support
  //   [7:7]   Decode assists support
  //   [9:8]   Reserved
  //   [10:10] Pause filter support
  //   [11:11] Reserved
  //   [12:12] Pause filter threshold support
  //   [31:13] Reserved

  leaf->edx = BX_CPUID_SVM_NESTED_PAGING |
              BX_CPUID_SVM_LBR_VIRTUALIZATION |
              BX_CPUID_SVM_SVM_LOCK;
}

so you've got an idea how to extend it

Stanislav

[stlw]

small correction - NRIP is already included in bx_generic - so you could use it if you enbale SVM.

just set cpu: model=bx_generic and you will have access to leaf CPUID of Bochs options.
See example:

#cpuid: x86_64=1, mmx=1, sep=1, sse=sse4_2, apic=xapic, aes=1, movbe=1, xsave=1
#cpuid: family=6, model=0x1a, stepping=5

configure list of options you want to have (if you have some conficts it will report you when you run Bochs).
use svm=1

Stanislav