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

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Date:   Fri, 3 Jul 2020 00:24:06 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        <xen-devel@...ts.xenproject.org>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Stefano Stabellini <sstabellini@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 1/4] x86/xen: remove 32-bit Xen PV guest support

On 02/07/2020 23:59, Boris Ostrovsky wrote:
> On 7/1/20 7:06 AM, Juergen Gross wrote:
>>  
>> -#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.

The hypercall path is a SYSCALL (and SYSRET out).

The "writeable" PTE path is a #PF, followed by an x86 instruction
emulation, which then reaches the same logic as the hypercall path (and
an IRET out).

~Andrew