linux-kernel - Re: [PATCH 19/19] vfio/pci: Implement huge

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Message-ID: <20240814132508.GM2032816@nvidia.com>
Date: Wed, 14 Aug 2024 10:25:08 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Peter Xu <peterx@...hat.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Sean Christopherson <seanjc@...gle.com>,
	Oscar Salvador <osalvador@...e.de>,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
	Will Deacon <will@...nel.org>, Gavin Shan <gshan@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>, Zi Yan <ziy@...dia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Alistair Popple <apopple@...dia.com>,
	Borislav Petkov <bp@...en8.de>,
	David Hildenbrand <david@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, kvm@...r.kernel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Yan Zhao <yan.y.zhao@...el.com>
Subject: Re: [PATCH 19/19] vfio/pci: Implement huge_fault support

On Fri, Aug 09, 2024 at 12:09:09PM -0400, Peter Xu wrote:
> @@ -1672,30 +1679,49 @@ static vm_fault_t vfio_pci_mmap_fault(struct vm_fault *vmf)
>  	if (vdev->pm_runtime_engaged || !__vfio_pci_memory_enabled(vdev))
>  		goto out_unlock;
>  
> -	ret = vmf_insert_pfn(vma, vmf->address, pfn + pgoff);
> -	if (ret & VM_FAULT_ERROR)
> -		goto out_unlock;
> -
> -	/*
> -	 * Pre-fault the remainder of the vma, abort further insertions and
> -	 * supress error if fault is encountered during pre-fault.
> -	 */
> -	for (; addr < vma->vm_end; addr += PAGE_SIZE, pfn++) {
> -		if (addr == vmf->address)
> -			continue;
> -
> -		if (vmf_insert_pfn(vma, addr, pfn) & VM_FAULT_ERROR)
> -			break;
> +	switch (order) {
> +	case 0:
> +		ret = vmf_insert_pfn(vma, vmf->address, pfn + pgoff);
> +		break;
> +#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
> +	case PMD_ORDER:
> +		ret = vmf_insert_pfn_pmd(vmf, __pfn_to_pfn_t(pfn + pgoff,
> +							     PFN_DEV), false);
> +		break;
> +#endif
> +#ifdef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP
> +	case PUD_ORDER:
> +		ret = vmf_insert_pfn_pud(vmf, __pfn_to_pfn_t(pfn + pgoff,
> +							     PFN_DEV), false);
> +		break;
> +#endif

I feel like this switch should be in some general function? 

vmf_insert_pfn_order(vmf, order, __pfn_to_pfn_t(pfn + pgoff, PFN_DEV), false);

No reason to expose every driver to this when you've already got a
nice contract to have the driver work on the passed in order.

What happens if the driver can't get a PFN that matches the requested
order?

Jason