[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH 0/2] expose host-phys-bits to guest
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH 0/2] expose host-phys-bits to guest |
Date: |
Sun, 4 Sep 2022 16:37:59 -0400 |
On Fri, Sep 02, 2022 at 10:44:20AM +0200, Gerd Hoffmann wrote:
> Hi,
>
> > I feel there are three major sources of controversy here
> >
> > 0. the cover letter and subject don't do such a good job
> > explaining that what we are doing is just telling guest
> > CPUID is not broken. we are not exposing anything new
> > and not exposing host capability to guest, for example,
> > if cpuid phys address is smaller than host things also
> > work fine.
> >
> > 1. really the naming. We need to be more explicit that it's just a bugfix.
>
> Yep, I'll go improve that for v2.
>
> > 2. down the road we will want to switch the default when no PV. however,
> > some hosts might still want conservative firmware for compatibility
> > reasons, so I think we need a way to tell firmware
> > "ignore phys address width in CPUID like you did in the past".
> > let's add a flag for that?
> > and if none are set firmware should print a warning, though I
> > do not know how many people will see that. Maybe some ;)
>
> > /*
> > * Force firmware to be very conservative in its use of physical
> > * addresses, ignoring phys address width in CPUID.
> > * Helpful for migration between hosts with different capabilities.
> > */
> > #define KVM_BUG_PHYS_ADDRESS_WIDTH_BROKEN 2
>
> I don't see a need for that. Live migration compatibility can be
> handled just fine today using
> 'host-phys-bits=on,host-phys-bits-limit=<xx>'
>
> Which is simliar to 'phys-bits=<xx>'.
yes but what if user did not configure anything?
the point of the above is so we can eventually, in X years, change the guests
to trust CPUID by default.
> The important difference is that phys-bits allows pretty much anything
> whereas host-phys-bits-limit applies sanity checks against the host
> supported phys bits and throws error on invalid values.
>
> take care,
> Gerd
- Re: [PATCH 0/2] expose host-phys-bits to guest, Xiaoyao Li, 2022/09/01
- Re: [PATCH 0/2] expose host-phys-bits to guest, Gerd Hoffmann, 2022/09/01
- Re: [PATCH 0/2] expose host-phys-bits to guest, Xiaoyao Li, 2022/09/01
- Re: [PATCH 0/2] expose host-phys-bits to guest, Gerd Hoffmann, 2022/09/01
- Re: [PATCH 0/2] expose host-phys-bits to guest, Xiaoyao Li, 2022/09/01
- Re: [PATCH 0/2] expose host-phys-bits to guest, Gerd Hoffmann, 2022/09/02
- Re: [PATCH 0/2] expose host-phys-bits to guest, Michael S. Tsirkin, 2022/09/02
- Re: [PATCH 0/2] expose host-phys-bits to guest, Gerd Hoffmann, 2022/09/02
- Re: [PATCH 0/2] expose host-phys-bits to guest,
Michael S. Tsirkin <=
- Re: [PATCH 0/2] expose host-phys-bits to guest, Gerd Hoffmann, 2022/09/05
Re: [PATCH 0/2] expose host-phys-bits to guest, Claudio Fontana, 2022/09/01