Messages in this thread | | | Subject | Re: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN_PV | From | Juergen Gross <> | Date | Fri, 19 Nov 2021 11:27:39 +0100 |
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On 19.11.21 11:20, Kirill A. Shutemov wrote: > On Fri, Nov 19, 2021 at 03:51:44PM +0800, Lai Jiangshan wrote: >> 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. > > That's very vague statement. > > Could you elaborate on what is wrong with proposed fix? > >> 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 > > It pollutes namespace for no particular reason. I don't see it justified. >
I agree. IMO weak symbols should be avoided if easily possible, and the patch here shows that it IS possible without any problem.
Juergen [unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature] | |