On 5/24/23 3:44 PM, Tian, Kevin wrote:
From: Liu, Yi L yi.l.liu@intel.com Sent: Thursday, May 11, 2023 10:51 PM
From: Lu Baolu baolu.lu@linux.intel.com
When remapping hardware is configured by system software in scalable mode as Nested (PGTT=011b) and with PWSNP field Set in the PASID-table-entry, it may Set Accessed bit and Dirty bit (and Extended Access bit if enabled) in first-stage page-table entries even when second-stage mappings indicate that corresponding first-stage page-table is Read-Only.
As the result, contents of pages designated by VMM as Read-Only can be modified by IOMMU via PML5E (PML4E for 4-level tables) access as part of address translation process due to DMAs issued by Guest.
Disallow the nested translation when there are read-only pages in the corresponding second-stage mappings. And, no read-only pages are allowed to be configured in the second-stage table of a nested translation. For the latter, an alternative is to disallow read-only mappings in any stage-2 domain as long as it's ever been used as a parent. In this way, we can simply replace the user counter with a flag.
In concept if the user understands this errata and does expect to enable nested translation it should never install any RO mapping in stage-2 in the entire VM life cycle."
IMHO the alternative is reasonable and simpler. If the user decides to enable nesting it should keep the nesting-friendly configuration static since whether nesting is enabled on a device is according to viommu configuration (i.e. whether the guest attaches the device to identity domain or non-identity domain) and it's not good to break the nesting setup just because the host inadvertently adds a RO mapping to s2 in the middle between guest is detached/put back to identity domain and then re-attach to an unmanaged domain.
Fair enough.
- if (!(prot & DMA_PTE_WRITE) && !domain->read_only_mapped) {
spin_lock_irqsave(&domain->lock, flags);if (domain->nested_users > 0) {spin_unlock_irqrestore(&domain->lock, flags);return -EINVAL;}this is worth a one-off warning. Same in the other path.
Sure.
Best regards, baolu