[Xen-changelog] [xen master] xen/x86: Replace mandatory barriers with compiler barriers

[patchbot@xxxxxxx]

commit d0291f3391ab34b34092fcdc56abd8153cbe4579
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Aug 16 18:07:27 2017 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Mon Sep 11 17:14:09 2017 +0100

    xen/x86: Replace mandatory barriers with compiler barriers
    
    In this case, rmb() is being used for its compiler barrier property.  
Replace
    it with an explicit barrer() and comment, to avoid it becoming an 
unnecessary
    lfence instruction (when rmb() gets fixed) or looking like an SMP issue.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/drivers/passthrough/amd/iommu_init.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/amd/iommu_init.c 
b/xen/drivers/passthrough/amd/iommu_init.c
index a459e99..474992a 100644
--- a/xen/drivers/passthrough/amd/iommu_init.c
+++ b/xen/drivers/passthrough/amd/iommu_init.c
@@ -558,7 +558,7 @@ static void parse_event_log_entry(struct amd_iommu *iommu, 
u32 entry[])
             return;
         }
         udelay(1);
-        rmb();
+        barrier(); /* Prevent hoisting of the entry[] read. */
         code = get_field_from_reg_u32(entry[1], IOMMU_EVENT_CODE_MASK,
                                       IOMMU_EVENT_CODE_SHIFT);
     }
@@ -663,7 +663,7 @@ void parse_ppr_log_entry(struct amd_iommu *iommu, u32 
entry[])
             return;
         }
         udelay(1);
-        rmb();
+        barrier(); /* Prevent hoisting of the entry[] read. */
         code = get_field_from_reg_u32(entry[1], IOMMU_PPR_LOG_CODE_MASK,
                                       IOMMU_PPR_LOG_CODE_SHIFT);
     }
--
generated by git-patchbot for /home/xen/git/xen.git#master

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