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Date:   Thu, 12 Jan 2023 17:47:57 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Jinank Jain <jinankjain@linux.microsoft.com>
Cc:     jinankjain@microsoft.com, kys@microsoft.com,
        haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com,
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        kirill.shutemov@linux.intel.com, ak@linux.intel.com,
        sathyanarayanan.kuppuswamy@linux.intel.com,
        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, anrayabh@linux.microsoft.com,
        mikelley@microsoft.com
Subject: Re: [PATCH v10 5/5] x86/hyperv: Change interrupt vector for nested
 root partition
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References: <cover.1672639707.git.jinankjain@linux.microsoft.com>
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On Mon, Jan 02, 2023 at 07:12:55AM +0000, Jinank Jain wrote:
> Traditionally we have been using the HYPERVISOR_CALLBACK_VECTOR to relay

Who's "we"?

Please use passive voice in your commit message: no "we" or "I", etc,
and describe your changes in imperative mood.

Also, pls read section "2) Describe your changes" in
Documentation/process/submitting-patches.rst for more details.

Also, see section "Changelog" in
Documentation/process/maintainer-tip.rst

Bottom line is: personal pronouns are ambiguous in text, especially with
so many parties/companies/etc developing the kernel so let's avoid them
please.

> the VMBus interrupt. But this does not work in case of nested
> hypervisor. Microsoft Hypervisor reserves 0x31 to 0x34 as the interrupt
> vector range for VMBus and thus we have to use one of the vectors from
> that range and setup the IDT accordingly.
> 
> Signed-off-by: Jinank Jain <jinankjain@linux.microsoft.com>
> ---
>  arch/x86/include/asm/idtentry.h    |  2 ++
>  arch/x86/include/asm/irq_vectors.h |  6 ++++++
>  arch/x86/kernel/cpu/mshyperv.c     | 15 +++++++++++++++
>  arch/x86/kernel/idt.c              | 10 ++++++++++
>  drivers/hv/vmbus_drv.c             |  3 ++-
>  5 files changed, 35 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
> index 72184b0b2219..c0648e3e4d4a 100644
> --- a/arch/x86/include/asm/idtentry.h
> +++ b/arch/x86/include/asm/idtentry.h
> @@ -686,6 +686,8 @@ DECLARE_IDTENTRY_SYSVEC(POSTED_INTR_NESTED_VECTOR,	sysvec_kvm_posted_intr_nested
>  DECLARE_IDTENTRY_SYSVEC(HYPERVISOR_CALLBACK_VECTOR,	sysvec_hyperv_callback);
>  DECLARE_IDTENTRY_SYSVEC(HYPERV_REENLIGHTENMENT_VECTOR,	sysvec_hyperv_reenlightenment);
>  DECLARE_IDTENTRY_SYSVEC(HYPERV_STIMER0_VECTOR,	sysvec_hyperv_stimer0);
> +DECLARE_IDTENTRY_SYSVEC(HYPERV_INTR_NESTED_VMBUS_VECTOR,
> +			sysvec_hyperv_nested_vmbus_intr);
>  #endif
>  
>  #if IS_ENABLED(CONFIG_ACRN_GUEST)
> diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
> index 43dcb9284208..729d19eab7f5 100644
> --- a/arch/x86/include/asm/irq_vectors.h
> +++ b/arch/x86/include/asm/irq_vectors.h
> @@ -102,6 +102,12 @@
>  #if IS_ENABLED(CONFIG_HYPERV)
>  #define HYPERV_REENLIGHTENMENT_VECTOR	0xee
>  #define HYPERV_STIMER0_VECTOR		0xed
> +/*
> + * FIXME: Change this, once Microsoft Hypervisor changes its assumption
      ^^^^^^

This patch looks like it is not ready to go anywhere yet...

> + * around VMBus interrupt vector allocation for nested root partition.

When is that going to happen? If at all...

> + * Or provides a better interface to detect this instead of hardcoding.
> + */
> +#define HYPERV_INTR_NESTED_VMBUS_VECTOR	0x31
>  #endif
>  
>  #define LOCAL_TIMER_VECTOR		0xec
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 938fc82edf05..4dfe0f9d7be3 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -126,6 +126,21 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
>  	set_irq_regs(old_regs);
>  }
>  
> +DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_nested_vmbus_intr)
> +{
> +	struct pt_regs *old_regs = set_irq_regs(regs);
> +
> +	inc_irq_stat(irq_hv_callback_count);
> +
> +	if (vmbus_handler)
> +		vmbus_handler();
> +
> +	if (ms_hyperv.hints & HV_DEPRECATING_AEOI_RECOMMENDED)
> +		ack_APIC_irq();
> +
> +	set_irq_regs(old_regs);
> +}
> +
>  void hv_setup_vmbus_handler(void (*handler)(void))
>  {
>  	vmbus_handler = handler;
> diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
> index a58c6bc1cd68..3536935cea39 100644
> --- a/arch/x86/kernel/idt.c
> +++ b/arch/x86/kernel/idt.c
> @@ -160,6 +160,16 @@ static const __initconst struct idt_data apic_idts[] = {
>  # endif
>  	INTG(SPURIOUS_APIC_VECTOR,		asm_sysvec_spurious_apic_interrupt),
>  	INTG(ERROR_APIC_VECTOR,			asm_sysvec_error_interrupt),
> +#ifdef CONFIG_HYPERV
> +	/*
> +	 * This is a hack because we cannot install this interrupt handler
> +	 * via alloc_intr_gate as it does not allow interrupt vector less
> +	 * than FIRST_SYSTEM_VECTORS. And hyperv does not want anything other
> +	 * than 0x31-0x34 as the interrupt vector for vmbus interrupt in case

Well:

/*
 * IDT vectors usable for external interrupt sources start at 0x20.
 * (0x80 is the syscall vector, 0x30-0x3f are for ISA)
				^^^^^^^^^^^^^^^^^^^^^^

 */
#define FIRST_EXTERNAL_VECTOR		0x20

I guess HyperV decided to reuse those...?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette