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From: Launchpad Bug Tracker <1904317@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1904317] Re: cpu feature selection is not affected to guest 's cpuid with whpx
Date: Sat, 10 Jul 2021 04:17:16 -0000	[thread overview]
Message-ID: <162589063741.5654.18281374532182514802.malone@loganberry.canonical.com> (raw)
In-Reply-To: 160543118215.29327.13808899207251644228.malonedeb@wampee.canonical.com

[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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      parent reply	other threads:[~2021-07-10  4:38 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-15  9:06 [Bug 1904317] [NEW] cpu feature selection is not affected to guest 's cpuid with whpx Takumi Nakamura
2020-11-16 11:53 ` Philippe Mathieu-Daudé
2020-11-16 11:53   ` Philippe Mathieu-Daudé
2021-05-10  4:25 ` [Bug 1904317] " Thomas Huth
2021-07-10  4:17 ` Launchpad Bug Tracker [this message]

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