linux-kernel - Re: [PATCH V4] PCI: Extend ACS configurability

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Date: Wed, 26 Jun 2024 08:50:03 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Vidya Sagar <vidyas@...dia.com>, "corbet@....net" <corbet@....net>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"galshalom@...dia.com" <galshalom@...dia.com>,
	"leonro@...dia.com" <leonro@...dia.com>,
	"treding@...dia.com" <treding@...dia.com>,
	"jonathanh@...dia.com" <jonathanh@...dia.com>,
	"mmoshrefjava@...dia.com" <mmoshrefjava@...dia.com>,
	"shahafs@...dia.com" <shahafs@...dia.com>,
	"vsethi@...dia.com" <vsethi@...dia.com>,
	"sdonthineni@...dia.com" <sdonthineni@...dia.com>,
	"jan@...dia.com" <jan@...dia.com>,
	"Dave, Tushar" <tdave@...dia.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kthota@...dia.com" <kthota@...dia.com>,
	"mmaddireddy@...dia.com" <mmaddireddy@...dia.com>,
	"sagar.tv@...il.com" <sagar.tv@...il.com>
Subject: Re: [PATCH V4] PCI: Extend ACS configurability

On Wed, Jun 26, 2024 at 07:40:31AM +0000, Tian, Kevin wrote:
> > From: Vidya Sagar <vidyas@...dia.com>
> > Sent: Tuesday, June 25, 2024 11:32 PM
> > 
> > PCIe ACS settings control the level of isolation and the possible P2P
> > paths between devices. With greater isolation the kernel will create
> > smaller iommu_groups and with less isolation there is more HW that
> > can achieve P2P transfers. From a virtualization perspective all
> > devices in the same iommu_group must be assigned to the same VM as
> > they lack security isolation.
> > 
> 
> It'll be helpful to also call out the impact of losing other features (e.g. PASID)
> with less isolation:
> 
> pci_enable_pasid()
> {
> 	...
> 	if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
> 		return -EINVAL;
> 	...
> }

Yeah, that is one of the considerations that might go into using
asymmetric ACS..

Jason