Mailing List Archive

All hardware with VT-d has CMPXCHG16B support. Check this at initialisation
time, and remove the effectively-dead logic for the non-cx16 case.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Teddy Astie <teddy.astie@vates.tech>
---
xen/drivers/passthrough/vtd/iommu.c | 73 ++++++++++-------------------
1 file changed, 25 insertions(+), 48 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index c7110af7c9..9c787ba9eb 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1482,7 +1482,7 @@ int domain_context_mapping_one(
{
struct domain_iommu *hd = dom_iommu(domain);
struct context_entry *context, *context_entries, lctxt;
- __uint128_t old;
+ __uint128_t res, old;
uint64_t maddr;
uint16_t seg = iommu->drhd->segment, prev_did = 0;
struct domain *prev_dom = NULL;
@@ -1580,55 +1580,23 @@ int domain_context_mapping_one(
ASSERT(!context_fault_disable(lctxt));
}

- if ( cpu_has_cx16 )
- {
- __uint128_t res = cmpxchg16b(context, &old, &lctxt.full);
-
- /*
- * Hardware does not update the context entry behind our backs,
- * so the return value should match "old".
- */
- if ( res != old )
- {
- if ( pdev )
- check_cleanup_domid_map(domain, pdev, iommu);
- printk(XENLOG_ERR
- "%pp: unexpected context entry %016lx_%016lx (expected %016lx_%016lx)\n",
- &PCI_SBDF(seg, bus, devfn),
- (uint64_t)(res >> 64), (uint64_t)res,
- (uint64_t)(old >> 64), (uint64_t)old);
- rc = -EILSEQ;
- goto unlock;
- }
- }
- else if ( !prev_dom || !(mode & MAP_WITH_RMRR) )
- {
- context_clear_present(*context);
- iommu_sync_cache(context, sizeof(*context));
+ res = cmpxchg16b(context, &old, &lctxt.full);

- write_atomic(&context->hi, lctxt.hi);
- /* No barrier should be needed between these two. */
- write_atomic(&context->lo, lctxt.lo);
- }
- else /* Best effort, updating DID last. */
+ /*
+ * Hardware does not update the context entry behind our backs,
+ * so the return value should match "old".
+ */
+ if ( res != old )
{
- /*
- * By non-atomically updating the context entry's DID field last,
- * during a short window in time TLB entries with the old domain ID
- * but the new page tables may be inserted. This could affect I/O
- * of other devices using this same (old) domain ID. Such updating
- * therefore is not a problem if this was the only device associated
- * with the old domain ID. Diverting I/O of any of a dying domain's
- * devices to the quarantine page tables is intended anyway.
- */
- if ( !(mode & (MAP_OWNER_DYING | MAP_SINGLE_DEVICE)) )
- printk(XENLOG_WARNING VTDPREFIX
- " %pp: reassignment may cause %pd data corruption\n",
- &PCI_SBDF(seg, bus, devfn), prev_dom);
-
- write_atomic(&context->lo, lctxt.lo);
- /* No barrier should be needed between these two. */
- write_atomic(&context->hi, lctxt.hi);
+ if ( pdev )
+ check_cleanup_domid_map(domain, pdev, iommu);
+ printk(XENLOG_ERR
+ "%pp: unexpected context entry %016lx_%016lx (expected %016lx_%016lx)\n",
+ &PCI_SBDF(seg, bus, devfn),
+ (uint64_t)(res >> 64), (uint64_t)res,
+ (uint64_t)(old >> 64), (uint64_t)old);
+ rc = -EILSEQ;
+ goto unlock;
}

iommu_sync_cache(context, sizeof(struct context_entry));
@@ -2630,6 +2598,15 @@ static int __init cf_check vtd_setup(void)
int ret;
bool reg_inval_supported = true;

+ if ( unlikely(!cpu_has_cx16) )
+ {
+ printk(XENLOG_ERR VTDPREFIX
+ "IOMMU: CPU doesn't support CMPXCHG16B, disabling\n");
+
+ ret = -ENODEV;
+ goto error;
+ }
+
if ( list_empty(&acpi_drhd_units) )
{
ret = -ENODEV;
--
2.44.0



Teddy Astie | Vates XCP-ng Intern

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech