On 6/12/2025 1:57 PM, Ethan MILON wrote:
Hi, On 5/2/25 4:16 AM, Alejandro Jimenez wrote:Caution: External email. Do not open attachments or click links, unless this email comes from a known sender and you know the content is safe. A guest must issue an INVALIDATE_DEVTAB_ENTRY command after changing a Device Table entry (DTE) e.g. after attaching a device and setting up its DTE. When intercepting this event, determine if the DTE has been configured for paging or not, and toggle the appropriate memory regions to allow DMA address translation for the address space if needed. Requires dma-remap=on. Signed-off-by: Alejandro Jimenez <alejandro.j.jime...@oracle.com> --- hw/i386/amd_iommu.c | 78 +++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 76 insertions(+), 2 deletions(-) diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c index a2df73062bf7..75a92067f35f 100644 --- a/hw/i386/amd_iommu.c +++ b/hw/i386/amd_iommu.c @@ -991,18 +991,92 @@ static void amdvi_switch_address_space_all(AMDVIState *s) } } +/* + * A guest driver must issue the INVALIDATE_DEVTAB_ENTRY command to the IOMMU + * after changing a Device Table entry. We can use this fact to detect when a + * Device Table entry is created for a device attached to a paging domain and + * enable the corresponding IOMMU memory region to allow for DMA translation if + * appropriate. + */ +static void amdvi_update_addr_translation_mode(AMDVIState *s, uint16_t devid) +{ + uint8_t bus_num, devfn, dte_mode; + AMDVIAddressSpace *as; + uint64_t dte[4] = { 0 }; + IOMMUNotifier *n; + int ret; + + /* + * Convert the devid encoded in the command to a bus and devfn in + * order to retrieve the corresponding address space. + */ + bus_num = PCI_BUS_NUM(devid); + devfn = devid & 0xff; + + /* + * The main buffer of size (AMDVIAddressSpace *) * (PCI_BUS_MAX) has already + * been allocated within AMDVIState, but must be careful to not access + * unallocated devfn. + */ + if (!s->address_spaces[bus_num] || !s->address_spaces[bus_num][devfn]) { + return; + } + as = s->address_spaces[bus_num][devfn]; + + ret = amdvi_as_to_dte(as, dte); + + if (!ret) { + dte_mode = (dte[0] >> AMDVI_DEV_MODE_RSHIFT) & AMDVI_DEV_MODE_MASK; + } + + if ((ret < 0) || (!ret && !dte_mode)) { + /* + * The DTE could not be retrieved, it is not valid, or it is not setup + * for paging. In either case, ensure that if paging was previously in + * use then invalidate all existing mappings and then switch to use the + * no_dma memory region. + */If the DTE is malformed or could not be retrieved, wouldn't it be safer to default to the DMA region rather than falling back to direct access? Or am I missing something?
Hi Ethan I also agree with you. I think right way should be keep the IOMMU DMA region if error codes are AMDVI_FR_DTE_RTR_ERR and AMDVI_FR_DTE_TV. Otherwise when error code is AMDVI_FR_DTE_V, switch to direct access. @vasant what do you think ? Thanks Sairaj
