[xen stable-4.17] x86/pvh: fix identity mapping of low 1MB

[patchbot@xxxxxxx]

commit f6996645d2d66505b6f57cf17bcad726431043a0
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Tue Nov 14 13:55:23 2023 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Nov 14 13:55:23 2023 +0100

    x86/pvh: fix identity mapping of low 1MB
    
    The mapping of memory regions below the 1MB mark was all done by the PVH 
dom0
    builder code, causing the region to be avoided by the arch specific IOMMU
    hardware domain initialization code.  That lead to the IOMMU being enabled
    without reserved regions in the low 1MB identity mapped in the p2m for PVH
    hardware domains.  Firmware which happens to be missing RMRR/IVMD ranges
    describing E820 reserved regions in the low 1MB would transiently trigger 
IOMMU
    faults until the p2m is populated by the PVH dom0 builder:
    
    AMD-Vi: IO_PAGE_FAULT: 0000:00:13.1 d0 addr 00000000000eb380 flags 0x20 RW
    AMD-Vi: IO_PAGE_FAULT: 0000:00:13.1 d0 addr 00000000000eb340 flags 0
    AMD-Vi: IO_PAGE_FAULT: 0000:00:13.2 d0 addr 00000000000ea1c0 flags 0
    AMD-Vi: IO_PAGE_FAULT: 0000:00:14.5 d0 addr 00000000000eb480 flags 0x20 RW
    AMD-Vi: IO_PAGE_FAULT: 0000:00:12.0 d0 addr 00000000000eb080 flags 0x20 RW
    AMD-Vi: IO_PAGE_FAULT: 0000:00:14.5 d0 addr 00000000000eb400 flags 0
    AMD-Vi: IO_PAGE_FAULT: 0000:00:12.0 d0 addr 00000000000eb040 flags 0
    
    Those errors have been observed on the osstest pinot{0,1} boxes (AMD Fam15h
    Opteron(tm) Processor 3350 HE).
    
    Rely on the IOMMU arch init code to create any identity mappings for 
reserved
    regions in the low 1MB range (like it already does for reserved regions
    elsewhere), and leave the mapping of any holes to be performed by the dom0
    builder code.
    
    Fixes: 6b4f6a31ace1 ('x86/PVH: de-duplicate mappings for first Mb of Dom0 
memory')
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 4bb882fe6e4430782101fe06379649df1bbd458a
    master date: 2023-10-19 09:52:43 +0200
---
 xen/arch/x86/hvm/dom0_build.c       | 7 ++++---
 xen/drivers/passthrough/x86/iommu.c | 8 +-------
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
index 3ac6b7b423..c539a8d2c1 100644
--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -460,7 +460,7 @@ static int __init pvh_populate_p2m(struct domain *d)
         }
     }
 
-    /* Non-RAM regions of space below 1MB get identity mapped. */
+    /* Identity map everything below 1MB that's not already mapped. */
     for ( i = rc = 0; i < MB1_PAGES; ++i )
     {
         p2m_type_t p2mt;
@@ -470,8 +470,9 @@ static int __init pvh_populate_p2m(struct domain *d)
             rc = set_mmio_p2m_entry(d, _gfn(i), _mfn(i), PAGE_ORDER_4K);
         else
             /*
-             * If the p2m entry is already set it must belong to a RMRR and
-             * already be identity mapped, or be a RAM region.
+             * If the p2m entry is already set it must belong to a reserved
+             * region (e.g. RMRR/IVMD) and be identity mapped, or else be a
+             * RAM region.
              */
             ASSERT(p2mt == p2m_ram_rw || mfn_eq(mfn, _mfn(i)));
         put_gfn(d, i);
diff --git a/xen/drivers/passthrough/x86/iommu.c 
b/xen/drivers/passthrough/x86/iommu.c
index 8bd0ccb2e9..22d67b4fd2 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -384,13 +384,7 @@ void __hwdom_init arch_iommu_hwdom_init(struct domain *d)
     max_pfn = (GB(4) >> PAGE_SHIFT) - 1;
     top = max(max_pdx, pfn_to_pdx(max_pfn) + 1);
 
-    /*
-     * First Mb will get mapped in one go by pvh_populate_p2m(). Avoid
-     * setting up potentially conflicting mappings here.
-     */
-    start = paging_mode_translate(d) ? PFN_DOWN(MB(1)) : 0;
-
-    for ( i = start, count = 0; i < top; )
+    for ( i = 0, start = 0, count = 0; i < top; )
     {
         unsigned long pfn = pdx_to_pfn(i);
         unsigned int perms = hwdom_iommu_map(d, pfn, max_pfn);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.17