linux-kernel - Re: [PATCH] iommu/amd: Fix failure return from snp_lookup

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Date: Tue, 6 Feb 2024 12:31:25 +0100
From: Borislav Petkov <bp@...en8.de>
To: Ashish Kalra <Ashish.Kalra@....com>
Cc: x86@...nel.org, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
	thomas.lendacky@....com, michael.roth@....com,
	dan.carpenter@...aro.org
Subject: Re: [PATCH] iommu/amd: Fix failure return from snp_lookup_rmpentry().

On Mon, Feb 05, 2024 at 09:06:54PM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> The patch f366a8dac1b8: "iommu/amd: Clean up RMP entries for IOMMU
> pages during SNP shutdown" (linux-next), leads to the following

Add this:

[alias]
        one = show -s --pretty='format:%h (\"%s\")'

to your .git/config so that when you do

$ git one f366a8dac1b8

it can give you the proper formatting for commit references:

f366a8dac1b8 ("iommu/amd: Clean up RMP entries for IOMMU pages during SNP shutdown")

> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 88bb08ae39b2..11340380111d 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3813,9 +3813,11 @@ static int iommu_page_make_shared(void *page)
>  		bool assigned;
>  
>  		ret = snp_lookup_rmpentry(pfn, &assigned, &level);
> -		if (ret)
> +		if (ret) {
>  			pr_warn("IOMMU PFN %lx RMP lookup failed, ret %d\n",
>  				pfn, ret);
> +			return ret;
> +		}

This one is incomplete and we should've caught this in review: any of
those failure cases here should return an error and not attempt to make
a pfn shared again.

Diff ontop:

---

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 11340380111d..480e7681f4f3 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3814,24 +3814,27 @@ static int iommu_page_make_shared(void *page)
 
 		ret = snp_lookup_rmpentry(pfn, &assigned, &level);
 		if (ret) {
-			pr_warn("IOMMU PFN %lx RMP lookup failed, ret %d\n",
-				pfn, ret);
+			pr_warn("IOMMU PFN %lx RMP lookup failed, ret %d\n", pfn, ret);
 			return ret;
 		}
 
-		if (!assigned)
-			pr_warn("IOMMU PFN %lx not assigned in RMP table\n",
-				pfn);
+		if (!assigned) {
+			pr_warn("IOMMU PFN %lx not assigned in RMP table\n", pfn);
+			return -EINVAL;
+		}
 
 		if (level > PG_LEVEL_4K) {
 			ret = psmash(pfn);
-			if (ret) {
-				pr_warn("IOMMU PFN %lx had a huge RMP entry, but attempted psmash failed, ret: %d, level: %d\n",
-					pfn, ret, level);
-			}
+			if (!ret)
+				goto done;
+
+			pr_warn("PSMASH failed for IOMMU PFN %lx huge RMP entry, ret: %d, level: %d\n",
+				pfn, ret, level);
+			return ret;
 		}
 	}
 
+done:
 	return rmp_make_shared(pfn, PG_LEVEL_4K);
 }
 
-- 
Regards/Gruss,
    Boris.

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