linux-kernel - Re: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN

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Date:   Sat, 20 Nov 2021 09:23:14 +0800
From:   Lai Jiangshan <jiangshanlai+lkml@...il.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        "VMware, Inc." <pv-drivers@...are.com>
Subject: Re: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN_PV

On Fri, Nov 19, 2021 at 6:20 PM Kirill A. Shutemov <kirill@...temov.name> wrote:

> > It is part of what CONFIG_PARAVIRT_XXL was designed for to enable
> > pv-aware INTERRUPT_RETURN.
>
> That's very vague statement.
>
> Could you elaborate on what is wrong with proposed fix?
>

Although CONFIG_PARAVIRT_XXL is enabled only when XEN, but they are
separated configs.  There is no wrong with the patch, but it is not
justified to narrow the scope of INTERRUPT_RETURN.

How about:

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index cebec95a7124..4459f853f77b 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -746,10 +746,16 @@ extern void default_banner(void);
 #define PARA_SITE(ptype, ops)  _PVSITE(ptype, ops, .quad, 8)
 #define PARA_INDIRECT(addr)    *addr(%rip)

+#ifdef CONFIG_XEN_PV
+#define XEN_IRET        "jmp xen_iret;"
+#else
+#define XEN_IRET        ""
+#endif
+
 #define INTERRUPT_RETURN                                               \
        ANNOTATE_RETPOLINE_SAFE;                                        \
        ALTERNATIVE_TERNARY("jmp *paravirt_iret(%rip);",                \
-               X86_FEATURE_XENPV, "jmp xen_iret;", "jmp native_iret;")
+               X86_FEATURE_XENPV, XEN_IRET, "jmp native_iret;")

 #ifdef CONFIG_DEBUG_ENTRY
 .macro PARA_IRQ_save_fl

And in the patch, INTERRUPT_RETURN is moved at the definition
of SWAPGS, but SWAPGS is going to be removed:

https://lore.kernel.org/lkml/20211026143436.19071-2-jiangshanlai@gmail.com/