Re: [Xen-devel] [PATCH RFC] x86/shim: Refresh pvshim_defconfig

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Fri, Jul 26, 2019 at 6:58 AM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> On 26/07/2019 13:55, Tamas K Lengyel wrote:
> > On Fri, Jul 26, 2019 at 4:11 AM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 
> > wrote:
> >> * Add a dependency so the shim gets rebuilt when pvshim_defconfig changes.
> >> * Default to the NULL scheduler now that it works with vcpu online/offline.
> >>
> >> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >> ---
> >> CC: Jan Beulich <JBeulich@xxxxxxxx>
> >> CC: Wei Liu <wl@xxxxxxx>
> >> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> >> CC: Juergen Gross <jgross@xxxxxxxx>
> >> CC: Dario Faggioli <dfaggioli@xxxxxxxx>
> >>
> >> This patch depends on Dario's series, and cant go in until then.
> >>
> >> Also RFC.
> >>
> >> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> >> CC: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> >>
> >> I tried turning off MEM_ACCESS, but I can't get Kconfig to actually turn it
> >> off in the build.  What is the deal with MEM_ACCESS_ALWAYS_ON ?  It makes 
> >> it
> >> impossible to turn MEM_ACCESS off, becaue it is selected by x86, which 
> >> leaves
> >> MEM_ACCESS enabled and unmodifiable.
> > We never made it configurable to have MEM_ACCESS be disabled on x86.
> > The option only exists because when I started moving vm_event to
> > common code it had to be disabled for ARM at first. Then it looks like
> > Stefano did make it configurable for ARM so there it can actually be
> > disabled.
>
> Is it something we could consider making configurable at this point?
> Its certainly something we'd want to turn off in the PV shim build.
>
> While thinking about it, it is specific to HVM guests, so ought to
> depend on CONFIG_HVM anyway, which might be the easiest way to exclude
> it for the PV shim build if we don't want to make it actively
> configurable yet.

Sure, I would Ack a patch that makes it configurable. There were some
works in the past to make mem_access for PV domains as well but that
was a while ago, I don't think anyone has interest in that anymore.
Making it depend on HVM for x86 builds sounds reasonable to me, not
sure if that would work for ARM though as I don't think it has HVM
config option. Anyway, if someone makes changes to this I would highly
prefer to get rid of the MEM_ACCESS_ALWAYS_ON config option as it's a
confusing option name.

Tamas

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