Re: [PATCH V5 1/4] x86/paravirt: Move halt paravirt calls under CONFIG_PARAVIRT

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Feb 20, 2025 at 09:16:25PM +0000, Vishal Annapurve wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> 
> CONFIG_PARAVIRT_XXL is mainly defined/used by XEN PV guests. For
> other VM guest types, features supported under CONFIG_PARAVIRT
> are self sufficient. CONFIG_PARAVIRT mainly provides support for
> TLB flush operations and time related operations.
> 
> For TDX guest as well, paravirt calls under CONFIG_PARVIRT meets
> most of its requirement except the need of HLT and SAFE_HLT
> paravirt calls, which is currently defined under
> CONFIG_PARAVIRT_XXL.
> 
> Since enabling CONFIG_PARAVIRT_XXL is too bloated for TDX guest
> like platforms, move HLT and SAFE_HLT paravirt calls under
> CONFIG_PARAVIRT.

Could you use the bloat-o-meter to give an idea of the savings?

Also .. aren't most distros building with Xen support so they will
always have the full paravirt support?

> 
> Moving HLT and SAFE_HLT paravirt calls are not fatal and should not
> break any functionality for current users of CONFIG_PARAVIRT.
> 
> Cc: stable@vger.kernel.org
> Fixes: bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests")
> Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Signed-off-by: Vishal Annapurve <vannapurve@google.com>
> ---
>  arch/x86/include/asm/irqflags.h       | 40 +++++++++++++++------------
>  arch/x86/include/asm/paravirt.h       | 20 +++++++-------
>  arch/x86/include/asm/paravirt_types.h |  3 +-
>  arch/x86/kernel/paravirt.c            | 14 ++++++----
>  4 files changed, 41 insertions(+), 36 deletions(-)
> 
> diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
> index cf7fc2b8e3ce..1c2db11a2c3c 100644
> --- a/arch/x86/include/asm/irqflags.h
> +++ b/arch/x86/include/asm/irqflags.h
> @@ -76,6 +76,28 @@ static __always_inline void native_local_irq_restore(unsigned long flags)
>  
>  #endif
>  
> +#ifndef CONFIG_PARAVIRT
> +#ifndef __ASSEMBLY__
> +/*
> + * Used in the idle loop; sti takes one instruction cycle
> + * to complete:
> + */
> +static __always_inline void arch_safe_halt(void)
> +{
> +	native_safe_halt();
> +}
> +
> +/*
> + * Used when interrupts are already enabled or to
> + * shutdown the processor:
> + */
> +static __always_inline void halt(void)
> +{
> +	native_halt();
> +}
> +#endif /* __ASSEMBLY__ */
> +#endif /* CONFIG_PARAVIRT */
> +
>  #ifdef CONFIG_PARAVIRT_XXL
>  #include <asm/paravirt.h>
>  #else
> @@ -97,24 +119,6 @@ static __always_inline void arch_local_irq_enable(void)
>  	native_irq_enable();
>  }
>  
> -/*
> - * Used in the idle loop; sti takes one instruction cycle
> - * to complete:
> - */
> -static __always_inline void arch_safe_halt(void)
> -{
> -	native_safe_halt();
> -}
> -
> -/*
> - * Used when interrupts are already enabled or to
> - * shutdown the processor:
> - */
> -static __always_inline void halt(void)
> -{
> -	native_halt();
> -}
> -
>  /*
>   * For spinlocks, etc:
>   */
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 041aff51eb50..29e7331a0c98 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -107,6 +107,16 @@ static inline void notify_page_enc_status_changed(unsigned long pfn,
>  	PVOP_VCALL3(mmu.notify_page_enc_status_changed, pfn, npages, enc);
>  }
>  
> +static __always_inline void arch_safe_halt(void)
> +{
> +	PVOP_VCALL0(irq.safe_halt);
> +}
> +
> +static inline void halt(void)
> +{
> +	PVOP_VCALL0(irq.halt);
> +}
> +
>  #ifdef CONFIG_PARAVIRT_XXL
>  static inline void load_sp0(unsigned long sp0)
>  {
> @@ -170,16 +180,6 @@ static inline void __write_cr4(unsigned long x)
>  	PVOP_VCALL1(cpu.write_cr4, x);
>  }
>  
> -static __always_inline void arch_safe_halt(void)
> -{
> -	PVOP_VCALL0(irq.safe_halt);
> -}
> -
> -static inline void halt(void)
> -{
> -	PVOP_VCALL0(irq.halt);
> -}
> -
>  static inline u64 paravirt_read_msr(unsigned msr)
>  {
>  	return PVOP_CALL1(u64, cpu.read_msr, msr);
> diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
> index fea56b04f436..abccfccc2e3f 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -120,10 +120,9 @@ struct pv_irq_ops {
>  	struct paravirt_callee_save save_fl;
>  	struct paravirt_callee_save irq_disable;
>  	struct paravirt_callee_save irq_enable;
> -
> +#endif
>  	void (*safe_halt)(void);
>  	void (*halt)(void);
> -#endif
>  } __no_randomize_layout;
>  
>  struct pv_mmu_ops {
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index 1ccaa3397a67..c5bb980b8a67 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -110,6 +110,11 @@ int paravirt_disable_iospace(void)
>  	return request_resource(&ioport_resource, &reserve_ioports);
>  }
>  
> +static noinstr void pv_native_safe_halt(void)
> +{
> +	native_safe_halt();
> +}
> +
>  #ifdef CONFIG_PARAVIRT_XXL
>  static noinstr void pv_native_write_cr2(unsigned long val)
>  {
> @@ -125,11 +130,6 @@ static noinstr void pv_native_set_debugreg(int regno, unsigned long val)
>  {
>  	native_set_debugreg(regno, val);
>  }
> -
> -static noinstr void pv_native_safe_halt(void)
> -{
> -	native_safe_halt();
> -}
>  #endif
>  
>  struct pv_info pv_info = {
> @@ -186,9 +186,11 @@ struct paravirt_patch_template pv_ops = {
>  	.irq.save_fl		= __PV_IS_CALLEE_SAVE(pv_native_save_fl),
>  	.irq.irq_disable	= __PV_IS_CALLEE_SAVE(pv_native_irq_disable),
>  	.irq.irq_enable		= __PV_IS_CALLEE_SAVE(pv_native_irq_enable),
> +#endif /* CONFIG_PARAVIRT_XXL */
> +
> +	/* Irq HLT ops. */
>  	.irq.safe_halt		= pv_native_safe_halt,
>  	.irq.halt		= native_halt,
> -#endif /* CONFIG_PARAVIRT_XXL */
>  
>  	/* Mmu ops. */
>  	.mmu.flush_tlb_user	= native_flush_tlb_local,
> -- 
> 2.48.1.601.g30ceb7b040-goog
> 
>