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

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Message-ID: <6d0b517a-6c53-61d3-117b-40e33e013037@oracle.com>
Date:   Thu, 2 Jul 2020 18:59:21 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH v2 1/4] x86/xen: remove 32-bit Xen PV guest support

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@...e.com>
> ---
>  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)



> @@ -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.


>  
> -#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.


> @@ -654,14 +621,12 @@ static int __xen_pgd_walk(struct mm_struct *mm, pgd_t *pgd,


Comment above should be updated.


-boris