linux-kernel - Re: [PATCH v5 2/6] iommu/amd: Introduce helper function to update 256-bit DTE

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Message-ID: <20241007140642.GP1365916@nvidia.com>
Date: Mon, 7 Oct 2024 11:06:42 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc: linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, joro@...tes.org,
	robin.murphy@....com, vasant.hegde@....com, kevin.tian@...el.com,
	jon.grimm@....com, santosh.shukla@....com, pandoh@...gle.com,
	kumaranand@...gle.com
Subject: Re: [PATCH v5 2/6] iommu/amd: Introduce helper function to update
 256-bit DTE

On Mon, Oct 07, 2024 at 04:13:49AM +0000, Suravee Suthikulpanit wrote:
> +static void write_dte_upper128(struct dev_table_entry *ptr, struct dev_table_entry *new)
> +{
> +	struct dev_table_entry old = {};
> +
> +	do {
> +		old.data128[1] = ptr->data128[1];
> +		new->data[2] &= ~DTE_DATA2_INTR_MASK;
> +		new->data[2] |= old.data[2] & (DTE_DATA2_INTR_MASK | DTE_DATA2_RESV_MASK);

Why preserve the reserved bits? Shouldn't they be reserved by forced
to 0? Should have a comment explaining this

> +static void iommu_flush_dte_sync(struct amd_iommu *iommu, u16 devid)
> +{

You might consider re-ordering to avoid the function forward
declaration.

Looks fine otherwise

Jason