linux-kernel - Re: [RFT][PATCH v2 5/9] vfio/ap: Remove redundant pfn

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Message-ID: <20220706175519.GM693670@nvidia.com>
Date:   Wed, 6 Jul 2022 14:55:19 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     kwankhede@...dia.com, corbet@....net, hca@...ux.ibm.com,
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Subject: Re: [RFT][PATCH v2 5/9] vfio/ap: Remove redundant pfn

On Tue, Jul 05, 2022 at 11:27:55PM -0700, Nicolin Chen wrote:
> The vfio_ap_ops code maintains both nib address and its PFN, which
> is redundant, merely because vfio_pin/unpin_pages API wanted pfn.
> Since vfio_pin/unpin_pages() now accept "iova", remove duplicated
> pfn code in their callers too.

I would describe this as renaming saved_pfn to saved_iova

>   *
>   * @vcpu: the object representing the vcpu executing the PQAP(AQIC) instruction.
>   * @nib: the location for storing the nib address.
> - * @g_pfn: the location for storing the page frame number of the page containing
> - *	   the nib.
>   *
>   * When the PQAP(AQIC) instruction is executed, general register 2 contains the
>   * address of the notification indicator byte (nib) used for IRQ notification.
> - * This function parses the nib from gr2 and calculates the page frame
> - * number for the guest of the page containing the nib. The values are
> - * stored in @nib and @g_pfn respectively.
> - *
> - * The g_pfn of the nib is then validated to ensure the nib address is valid.
> + * This function parses and validate the nib from gr2.
>   *
>   * Return: returns zero if the nib address is a valid; otherwise, returns
>   *	   -EINVAL.
>   */
> -static int vfio_ap_validate_nib(struct kvm_vcpu *vcpu, unsigned long *nib,
> -				unsigned long *g_pfn)
> +static int vfio_ap_validate_nib(struct kvm_vcpu *vcpu, dma_addr_t *nib)
>  {
>  	*nib = vcpu->run->s.regs.gprs[2];
> -	*g_pfn = *nib >> PAGE_SHIFT;
>  
> -	if (kvm_is_error_hva(gfn_to_hva(vcpu->kvm, *g_pfn)))
> +	if (kvm_is_error_hva(gfn_to_hva(vcpu->kvm, *nib >> PAGE_SHIFT)))
>  		return -EINVAL;

This existing code is fishy. nib is either an IOVA passed to
vfio_pin_pages() or a GFN passed to gfn_to_hva(). These are not the
same thing and are not interchangable - writing code like this assumes
that the guest is running with iommu=pt or no iommu.

Someone should look at it..

Otherwise it looks OK

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason