Re: [PATCH v2 1/4] x86/xen: remove 32-bit Xen PV guest support

[Jürgen Groß <jgross@xxxxxxxx>]

On 03.07.20 00:59, Boris Ostrovsky wrote:
> On 7/1/20 7:06 AM, Juergen Gross wrote:
> > Xen is requiring 64-bit machines today and since Xen 4.14 it can be
> > built without 32-bit PV guest support. There is no need to carry the
> > burden of 32-bit PV guest support in the kernel any longer, as new
> > guests can be either HVM or PVH, or they can use a 64 bit kernel.
> >
> > Remove the 32-bit Xen PV support from the kernel.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> >   arch/x86/entry/entry_32.S      | 109 +----------
> >   arch/x86/include/asm/proto.h   |   2 +-
> >   arch/x86/include/asm/segment.h |   2 +-
> >   arch/x86/kernel/head_32.S      |  31 ---
> >   arch/x86/xen/Kconfig           |   3 +-
> >   arch/x86/xen/Makefile          |   3 +-
> >   arch/x86/xen/apic.c            |  17 --
> >   arch/x86/xen/enlighten_pv.c    |  48 +----
>
> Should we drop PageHighMem() test in set_aliased_prot()?
>
>
> (And there are few other places where is is used, in mmu_pv.c)
Yes, will drop those.

> > @@ -555,13 +547,8 @@ static void xen_load_tls(struct thread_struct *t, unsigned 
> > int cpu)
> >          * exception between the new %fs descriptor being loaded and
> >          * %fs being effectively cleared at __switch_to().
> >          */
> > -       if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_CPU) {
> > -#ifdef CONFIG_X86_32
> > -               lazy_load_gs(0);
> > -#else
>
> I think this also needs an adjustment to the preceding comment.
Yes.

> >   
> > -#ifdef CONFIG_X86_PAE
> > -static void xen_set_pte_atomic(pte_t *ptep, pte_t pte)
> > -{
> > -       trace_xen_mmu_set_pte_atomic(ptep, pte);
> > -       __xen_set_pte(ptep, pte);
>
> Probably not for this series but I wonder whether __xen_set_pte() should
> continue to use hypercall now that we are 64-bit only.
As Andrew wrote already the hypercall will be cheaper.

I'll adjust the comment, though.

> > @@ -654,14 +621,12 @@ static int __xen_pgd_walk(struct mm_struct *mm, pgd_t 
> > *pgd,
>
> Comment above should be updated.
Yes.


Juergen