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    SubjectRe: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN_PV
    On Thu, Nov 18, 2021 at 7:14 AM Kirill A. Shutemov <kirill@shutemov.name> wrote:
    >
    > TDX is going to use CONFIG_PARAVIRT_XXL, but kernel fails to compile if
    > XEN_PV is not enabled:
    >
    > ld.lld: error: undefined symbol: xen_iret
    >
    > It happens because INTERRUPT_RETURN defined to use xen_iret if
    > CONFIG_PARAVIRT_XXL enabled regardless of CONFIG_XEN_PV.
    >
    > The issue is not visible in the current kernel because CONFIG_XEN_PV is
    > the only user of CONFIG_PARAVIRT_XXL and there's no way to enable them
    > separately.
    >
    > Rework code to define INTERRUPT_RETURN based on CONFIG_XEN_PV, not
    > CONFIG_PARAVIRT_XXL.
    >
    > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > Cc: Juergen Gross <jgross@suse.com>
    > Cc: Deep Shah <sdeep@vmware.com>
    > Cc: "VMware, Inc." <pv-drivers@vmware.com>
    > ---
    > arch/x86/include/asm/irqflags.h | 7 +++++--
    > arch/x86/include/asm/paravirt.h | 5 -----
    > 2 files changed, 5 insertions(+), 7 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
    > index b794b6da3214..3b8ddcb7be76 100644
    > --- a/arch/x86/include/asm/irqflags.h
    > +++ b/arch/x86/include/asm/irqflags.h
    > @@ -118,8 +118,6 @@ static __always_inline unsigned long arch_local_irq_save(void)
    > #define SAVE_FLAGS pushfq; popq %rax
    > #endif
    >
    > -#define INTERRUPT_RETURN jmp native_iret
    > -
    > #endif
    >
    > #endif /* __ASSEMBLY__ */
    > @@ -147,8 +145,13 @@ static __always_inline void arch_local_irq_restore(unsigned long flags)
    > #ifdef CONFIG_X86_64
    > #ifdef CONFIG_XEN_PV
    > #define SWAPGS ALTERNATIVE "swapgs", "", X86_FEATURE_XENPV
    > +#define INTERRUPT_RETURN \
    > + ANNOTATE_RETPOLINE_SAFE; \
    > + ALTERNATIVE_TERNARY("jmp *paravirt_iret(%rip);", \
    > + X86_FEATURE_XENPV, "jmp xen_iret;", "jmp native_iret;")

    It is part of what CONFIG_PARAVIRT_XXL was designed for to enable
    pv-aware INTERRUPT_RETURN.

    I would prefer xen_iret is defined as a weak symbol unconditionally.
    Like:

    diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
    index e38a4cf795d9..c0953f1b4559 100644
    --- a/arch/x86/entry/entry_64.S
    +++ b/arch/x86/entry/entry_64.S
    @@ -635,6 +635,7 @@ SYM_INNER_LABEL_ALIGN(native_iret, SYM_L_GLOBAL)
    jnz native_irq_return_ldt
    #endif

    +SYM_INNER_LABEL(xen_iret, SYM_L_WEAK) /* placeholder */
    SYM_INNER_LABEL(native_irq_return_iret, SYM_L_GLOBAL)
    /*
    * This may fault. Non-paranoid faults on return to userspace are
    It will work when !CONFIG_XEN_PV

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      Last update: 2021-11-19 08:52    [W:3.075 / U:0.540 seconds]
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