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Re: [PATCH v8 4/6] AMD/IOMMU: respect AtsDisabled device flag

On 28/09/2021 08:47, Jan Beulich wrote:
On 28.09.2021 09:34, Durrant, Paul wrote:
On 22/09/2021 15:37, Jan Beulich wrote:
IVHD entries may specify that ATS is to be blocked for a device or range
of devices. Honor firmware telling us so.

While adding respective checks I noticed that the 2nd conditional in
amd_iommu_setup_domain_device() failed to check the IOMMU's capability.
Add the missing part of the condition there, as no good can come from
enabling ATS on a device when the IOMMU is not capable of dealing with
ATS requests.

For actually using ACPI_IVHD_ATS_DISABLED, make its expansion no longer
exhibit UB.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
TBD: As an alternative to adding the missing IOMMU capability check, we
       may want to consider simply using dte->i in the 2nd conditional in
Note that while ATS enabling/disabling gets invoked without any locks
held, the two functions should not be possible to race with one another
for any individual device (or else we'd be in trouble already, as ATS
might then get re-enabled immediately after it was disabled, with the
DTE out of sync with this setting).
v7: New.

--- a/xen/drivers/passthrough/amd/iommu.h
+++ b/xen/drivers/passthrough/amd/iommu.h
@@ -120,6 +120,7 @@ struct ivrs_mappings {
       uint16_t dte_requestor_id;
       bool valid:1;
       bool dte_allow_exclusion:1;
+    bool block_ats:1;
/* ivhd device data settings */
       uint8_t device_flags;
--- a/xen/drivers/passthrough/amd/iommu_acpi.c
+++ b/xen/drivers/passthrough/amd/iommu_acpi.c
@@ -55,8 +55,8 @@ union acpi_ivhd_device {
static void __init add_ivrs_mapping_entry(
-    uint16_t bdf, uint16_t alias_id, uint8_t flags, bool alloc_irt,
-    struct amd_iommu *iommu)
+    uint16_t bdf, uint16_t alias_id, uint8_t flags, unsigned int ext_flags,
+    bool alloc_irt, struct amd_iommu *iommu)
       struct ivrs_mappings *ivrs_mappings = get_ivrs_mappings(iommu->seg);
@@ -66,6 +66,7 @@ static void __init add_ivrs_mapping_entr
       ivrs_mappings[bdf].dte_requestor_id = alias_id;
/* override flags for range of devices */
+    ivrs_mappings[bdf].block_ats = ext_flags & ACPI_IVHD_ATS_DISABLED;
       ivrs_mappings[bdf].device_flags = flags;

I'm assuming the above indentation problem (which appears to be repeated
in a few places below) is more to do with patch email generation rather
than the actual code modifications so...

Hmm, I first suspected a Thunderbird regression, but checking the list
archives I don't see any corruption. I'm therefore now suspecting the
problem may be at your end ...

It certainly could be; I was forced to upgrade my copy of Thunderbird recently. It's odd that the issue is not consistent though. As long as the actual code looks ok though... no problem.




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