[PATCH 4/4] iommu/x86: make unity range checking more strict

From: Roger Pau Monne <roger.pau@citrix.com>
To: xen-devel@lists.xenproject.org
Cc: Roger Pau Monne <roger.pau@citrix.com>,
	Jan Beulich <jbeulich@suse.com>, Paul Durrant <paul@xen.org>
Subject: [PATCH 4/4] iommu/x86: make unity range checking more strict
Date: Thu,  1 Feb 2024 18:01:59 +0100	[thread overview]
Message-ID: <20240201170159.66330-5-roger.pau@citrix.com> (raw)
In-Reply-To: <20240201170159.66330-1-roger.pau@citrix.com>

Currently when a unity range overlaps with memory being used as RAM by the
hypervisor the result would be that the IOMMU gets disabled.  However that's
not enough, as even with the IOMMU disabled the device will still access the
affected RAM areas.

Note that IVMD or RMRR ranges being placed over RAM is a firmware bug.

Doing so also allows to simplify the code and use a switch over the reported
memory type(s).

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
 xen/drivers/passthrough/x86/iommu.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/xen/drivers/passthrough/x86/iommu.c b/xen/drivers/passthrough/x86/iommu.c
index 63d4cb898218..9b977f84582f 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -806,10 +806,14 @@ bool __init iommu_unity_region_ok(mfn_t start, mfn_t end)
 
     for ( addr = start; !mfn_eq(addr, end); mfn_add(addr, 1) )
     {
-        unsigned int type = page_get_ram_type(addr);
-
-        if ( type == RAM_TYPE_UNKNOWN )
+        /*
+         * Any page that's at least partially of type RESERVED, UNUSABLE or
+         * ACPI will be considered by Xen of being all of that type, and hence
+         * the problematic pages are those that are fully holes or RAM.
+         */
+        switch ( page_get_ram_type(addr) )
         {
+        case RAM_TYPE_UNKNOWN:
             if ( e820_add_range(mfn_to_maddr(addr),
                                 mfn_to_maddr(addr) + PAGE_SIZE, E820_RESERVED) )
                 continue;
@@ -817,7 +821,10 @@ bool __init iommu_unity_region_ok(mfn_t start, mfn_t end)
                    "IOMMU: page at %#" PRI_mfn " couldn't be reserved\n",
                    mfn_x(addr));
             return false;
-        }
+
+        case RAM_TYPE_CONVENTIONAL:
+            panic("IOMMU: page at %#" PRI_mfn " overlaps RAM range\n",
+                  mfn_x(addr));
 
         /*
          * Types which aren't RAM are considered good enough.
@@ -825,14 +832,7 @@ bool __init iommu_unity_region_ok(mfn_t start, mfn_t end)
          * force Xen into assuming the whole page as having that type in
          * practice.
          */
-        if ( type & (RAM_TYPE_RESERVED | RAM_TYPE_ACPI |
-                     RAM_TYPE_UNUSABLE) )
-            continue;
-
-        printk(XENLOG_WARNING
-               "IOMMU: page at %#" PRI_mfn " can't be converted\n",
-               mfn_x(addr));
-        return false;
+        }
     }
 
     return true;
-- 
2.43.0


