[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Bug 1904317] [NEW] cpu feature selection is not affected to guest '
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [Bug 1904317] [NEW] cpu feature selection is not affected to guest 's cpuid with whpx |
Date: |
Mon, 16 Nov 2020 12:53:46 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 |
Cc'ing Sunil (WHPX maintainer).
On 11/15/20 10:06 AM, Takumi Nakamura wrote:
> 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
>