linux-kernel - Re: [PATCH v8 06/10] iommu/amd: Modify set_dte

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Message-ID: <20241101121022.GT10193@nvidia.com>
Date: Fri, 1 Nov 2024 09:10:22 -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 v8 06/10] iommu/amd: Modify set_dte_entry() to use
 256-bit DTE helpers

On Thu, Oct 31, 2024 at 06:42:39PM +0000, Suravee Suthikulpanit wrote:
> +struct dev_table_entry *amd_iommu_get_ivhd_dte_flags(u16 segid, u16 devid)
> +{
> +	struct ivhd_dte_flags *e;
> +	unsigned int best_len = UINT_MAX;
> +	struct dev_table_entry *dte = NULL;
> +
> +	for_each_ivhd_dte_flags(e) {
> +		/*
> +		 * Need to go through the whole list to find the smallest range,
> +		 * which contains the devid.
> +		 */
> +		if ((e->segid == segid) &&
> +		    (e->devid_first >= devid) &&
> +		    (e->devid_last <= devid)) {

Again, I don't know much about this format, but are you sure about
this logic? Consider:

 e->devid_first = 10
 devid = 12
 e->devid_last = 15

 (e->devid_first >= devid) == 10 >= 12 == FALSE
 (e->devid_last <= devid) == 15 <= 12 == FALSE

FALSE && FALSE == FALSE

It seems to me it does not do what the comment says? Compare to the
version I sent in my last email

Jason