linux-kernel - RE: [PATCH 3/4] iommu/sva: Support reservation of global PASIDs

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Date:   Mon, 6 Mar 2023 18:48:43 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
CC:     "Tian, Kevin" <kevin.tian@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>
Subject: RE: [PATCH 3/4] iommu/sva: Support reservation of global PASIDs

>> ENQCMDS does not have the restriction of using a single CPU MSR to store
>> PASIDs, PASID is supplied to the instruction operand. 
>
> Huh? That isn't what it says in the programming manual. It says the
> PASID only comes from the IA32_PASID msr and the only two operands are
> the destination MMIO and the memory source for the rest of the payload.

Jason,

Two different instructions with only one letter different in the name.

ENQCMD - ring 3 instruction. The PASID is inserted into the descriptor
pushed to the device from the IA32_PASID MSR.

ENQCMDS - ring 0 instruction (see that trailing "S" for Supervisor mode).
In this case the submitter can include any PASID value they want in the
in-memory copy of the descriptor and ENQCMDS will pass that to the
device.

-Tony