From: Takumi Nakamura <1904317@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1904317] [NEW] cpu feature selection is not affected to guest 's cpuid with whpx
Date: Sun, 15 Nov 2020 09:06:22 -0000 [thread overview]
Message-ID: <160543118215.29327.13808899207251644228.malonedeb@wampee.canonical.com> (raw)
Public bug reported:
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.
** Affects: qemu
Importance: Undecided
Status: New
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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:
New
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.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1904317/+subscriptions
next reply other threads:[~2020-11-15 9:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-15 9:06 Takumi Nakamura [this message]
2020-11-16 11:53 ` [Bug 1904317] [NEW] cpu feature selection is not affected to guest 's cpuid with whpx 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
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