linux-kernel - Re: [PATCH hyperv-next 6/6] drivers: SCSI: Do not bounce-bufffer for the confidential VMBus

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Message-ID: <20250409105332.GB5721@lst.de>
Date: Wed, 9 Apr 2025 12:53:32 +0200
From: Christoph Hellwig <hch@....de>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: aleksander.lobakin@...el.com, andriy.shevchenko@...ux.intel.com,
	arnd@...db.de, bp@...en8.de, catalin.marinas@....com,
	corbet@....net, dakr@...nel.org, dan.j.williams@...el.com,
	dave.hansen@...ux.intel.com, decui@...rosoft.com,
	gregkh@...uxfoundation.org, haiyangz@...rosoft.com, hch@....de,
	hpa@...or.com, James.Bottomley@...senPartnership.com,
	Jonathan.Cameron@...wei.com, kys@...rosoft.com, leon@...nel.org,
	lukas@...ner.de, luto@...nel.org, m.szyprowski@...sung.com,
	martin.petersen@...cle.com, mingo@...hat.com, peterz@...radead.org,
	quic_zijuhu@...cinc.com, robin.murphy@....com, tglx@...utronix.de,
	wei.liu@...nel.org, will@...nel.org, iommu@...ts.linux.dev,
	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org, linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	x86@...nel.org, apais@...rosoft.com, benhill@...rosoft.com,
	bperkins@...rosoft.com, sunilmut@...rosoft.com
Subject: Re: [PATCH hyperv-next 6/6] drivers: SCSI: Do not bounce-bufffer
 for the confidential VMBus

On Tue, Apr 08, 2025 at 05:08:35PM -0700, Roman Kisel wrote:
> The device bit that indicates that the device is capable of I/O
> with private pages lets avoid excessive copying in the Hyper-V
> SCSI driver.
> 
> Set that bit equal to the confidential external memory one to
> not bounce buffer

Drivers have absolutely no business telling this.  The need for bounce
buffering or not is a platform/IOMMU decision and not one specific to
a certain device or driver.