[Bug 1904317] Re: cpu feature selection is not affected to guest 's cpuid with whpx

[Launchpad Bug Tracker]

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1904317

Title:
  cpu feature selection is not affected to guest 's cpuid with whpx

Status in QEMU:
  Expired

Bug description:
  On windows with -accel whpx, "-cpu" is ignored without any messages.
  Guest recognizes features as same as host's.

  Confirmed on v5.2.0-rc1.

  I suggest qemu may do,

  - Warn with incompatible -cpu options were given.
  - Enhance cpuid handling.

  Background:
  I was investigated mmio and block copy issue in Linux kernel.
  I met a problem that Linux went ill for touching mmio with whpx. (not with 
tcg)
  I suspect erms(enhanced rep movs) might trigger.
  I tried to mask erms on qemu with -feature,erms, but it was ineffective.

  At last, I disabled erms manually, to tweak whpx-all.c to mask erms in
  cpuid.

  FYI, qemu with whpx from/to mmio, "rep movsb" does byte access regardless of 
erms.
  Linux kernel tends to choose not "rep movsq" but "rep movsb" with erms.

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