Re: [PATCH v5 01/12] x86/paravirt: Move halt paravirt calls under CONFIG_PARAVIRT

[Juergen Gross <jgross@suse.com>]

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On 17.08.21 15:16, Kuppuswamy, Sathyanarayanan wrote:
> 
> 
> On 8/17/21 5:50 AM, Juergen Gross wrote:
>> On 12.08.21 09:18, Borislav Petkov wrote:
>>> On Wed, Aug 04, 2021 at 11:13:18AM -0700, Kuppuswamy Sathyanarayanan 
>>> 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
>>>> COFNIG_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.
>>>>
>>>> Moving HLT and SAFE_HLT paravirt calls are not fatal and should not
>>>> break any functionality for current users of CONFIG_PARAVIRT.
>>>>
>>>> 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>
>>>> ---
>>>
>>> You need to do this before sending your patches:
>>>
>>> ./scripts/get_maintainer.pl /tmp/tdx.01
>>> Thomas Gleixner <tglx@linutronix.de> (maintainer:X86 ARCHITECTURE 
>>> (32-BIT AND 64-BIT),commit_signer:1/6=17%)
>>> Ingo Molnar <mingo@redhat.com> (maintainer:X86 ARCHITECTURE (32-BIT 
>>> AND 64-BIT))
>>> Borislav Petkov <bp@alien8.de> (maintainer:X86 ARCHITECTURE (32-BIT 
>>> AND 64-BIT),commit_signer:6/6=100%)
>>> x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT))
>>> "H. Peter Anvin" <hpa@zytor.com> (reviewer:X86 ARCHITECTURE (32-BIT 
>>> AND 64-BIT))
>>> Juergen Gross <jgross@suse.com> (supporter:PARAVIRT_OPS 
>>> INTERFACE,commit_signer:5/6=83%,authored:5/6=83%,added_lines:15/16=94%,removed_lines:38/39=97%) 
>>>
>>> Deep Shah <sdeep@vmware.com> (supporter:PARAVIRT_OPS INTERFACE)
>>> "VMware, Inc." <pv-drivers@vmware.com> (supporter:PARAVIRT_OPS 
>>> INTERFACE)
>>> ...
>>>
>>> and CC also the supporters - I'm pretty sure at least Juergen would like
>>> to be kept up-to-date on pv changes. I'll CC him and the others now and
>>> leave in the whole diff but make sure you do that in the future please.
>>>
>>>>   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            |  4 ++-
>>>>   4 files changed, 36 insertions(+), 31 deletions(-)
>>>>
>>>> diff --git a/arch/x86/include/asm/irqflags.h 
>>>> b/arch/x86/include/asm/irqflags.h
>>>> index c5ce9845c999..f3bb33b1715d 100644
>>>> --- a/arch/x86/include/asm/irqflags.h
>>>> +++ b/arch/x86/include/asm/irqflags.h
>>>> @@ -59,6 +59,28 @@ static inline __cpuidle void native_halt(void)
>>>>   #endif
>>>> +#ifndef CONFIG_PARAVIRT
>>>> +#ifndef __ASSEMBLY__
>>>> +/*
>>>> + * Used in the idle loop; sti takes one instruction cycle
>>>> + * to complete:
>>>> + */
>>>> +static inline __cpuidle void arch_safe_halt(void)
>>>> +{
>>>> +    native_safe_halt();
>>>> +}
>>>> +
>>>> +/*
>>>> + * Used when interrupts are already enabled or to
>>>> + * shutdown the processor:
>>>> + */
>>>> +static inline __cpuidle void halt(void)
>>>> +{
>>>> +    native_halt();
>>>> +}
>>>> +#endif /* __ASSEMBLY__ */
>>>> +#endif /* CONFIG_PARAVIRT */
>>>> +
>>>>   #ifdef CONFIG_PARAVIRT_XXL
>>>>   #include <asm/paravirt.h>
>>
>> Did you test this with CONFIG_PARAVIRT enabled and CONFIG_PARAVIRT_XXL
>> disabled?
>>
>> I'm asking because in this case I don't see where halt() and
>> arch_safe_halt() would be defined in case someone is including
>> asm/irqflags.h and not asm/paravirt.h.
> 
> We have tested both cases and did not hit any issues.
> 
> 1. CONFIG_PARAVIRT=y and  CONFIG_PARAVIRT_XXL=y
> 2. CONFIG_PARAVIRT=y and  CONFIG_PARAVIRT_XXL=n

I guess you have been lucky and all users of arch_safe_halt() and halt()
are directly or indirectly including asm/paravirt.h by other means.

There might be configs where this is not true, though.

In any case I believe you should fix your patch to let asm/irqflags.h
include asm/paravirt.h for the CONFIG_PARAVIRT case.


Juergen

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