Re: [PATCH v2 05/20] amd_iommu: Add helper function to extract the DTE

[Sairaj Kodilkar <sarunkod@amd.com>]

On 5/2/2025 7:45 AM, Alejandro Jimenez wrote:
> Extracting the DTE from a given AMDVIAddressSpace pointer structure is a
> common operation required for syncing the shadow page tables. Implement a
> helper to do it and check for common error conditions.
> 
> Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
> ---
>   hw/i386/amd_iommu.c | 45 ++++++++++++++++++++++++++++++++++++++++-----
>   1 file changed, 40 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
> index dff6f04c8651..5322a614f5d6 100644
> --- a/hw/i386/amd_iommu.c
> +++ b/hw/i386/amd_iommu.c
> @@ -77,6 +77,18 @@ typedef struct AMDVIIOTLBEntry {
>       uint64_t page_mask;         /* physical page size  */
>   } AMDVIIOTLBEntry;
>   
> +/*
> + * These 'fault' reasons have an overloaded meaning since they are not only
> + * intended for describing reasons that generate an IO_PAGE_FAULT as per the AMD
> + * IOMMU specification, but are also used to signal internal errors in the
> + * emulation code.
> + */
> +typedef enum AMDVIFaultReason {
> +    AMDVI_FR_DTE_RTR_ERR = 1,   /* Failure to retrieve DTE */
> +    AMDVI_FR_DTE_V,             /* DTE[V] = 0 */
> +    AMDVI_FR_DTE_TV,            /* DTE[TV] = 0 */
> +} AMDVIFaultReason;
> +
>   uint64_t amdvi_extended_feature_register(AMDVIState *s)
>   {
>       uint64_t feature = AMDVI_DEFAULT_EXT_FEATURES;
> @@ -492,6 +504,28 @@ static inline uint64_t amdvi_get_pte_entry(AMDVIState *s, uint64_t pte_addr,
>       return pte;
>   }
>   
> +static int amdvi_as_to_dte(AMDVIAddressSpace *as, uint64_t *dte)
> +{
> +    uint16_t devid = PCI_BUILD_BDF(as->bus_num, as->devfn);
> +    AMDVIState *s = as->iommu_state;
> +
> +    if (!amdvi_get_dte(s, devid, dte)) {
> +        /* Unable to retrieve DTE for devid */
> +        return -AMDVI_FR_DTE_RTR_ERR;
> +    }
> +
> +    if (!(dte[0] & AMDVI_DEV_VALID)) {
> +        /* DTE[V] not set, address is passed untranslated for devid */
> +        return -AMDVI_FR_DTE_V;
> +    }
> +
> +    if (!(dte[0] & AMDVI_DEV_TRANSLATION_VALID)) {
> +        /* DTE[TV] not set, host page table not valid for devid */
> +        return -AMDVI_FR_DTE_TV;
> +    }
> +    return 0;
> +}
> +
>   /* log error without aborting since linux seems to be using reserved bits */
>   static void amdvi_inval_devtab_entry(AMDVIState *s, uint64_t *cmd)
>   {
> @@ -1024,6 +1058,7 @@ static void amdvi_do_translate(AMDVIAddressSpace *as, hwaddr addr,
>       uint16_t devid = PCI_BUILD_BDF(as->bus_num, as->devfn);
>       AMDVIIOTLBEntry *iotlb_entry = amdvi_iotlb_lookup(s, addr, devid);
>       uint64_t entry[4];
> +    int dte_ret;
>   
>       if (iotlb_entry) {
>           trace_amdvi_iotlb_hit(PCI_BUS_NUM(devid), PCI_SLOT(devid),
> @@ -1035,13 +1070,13 @@ static void amdvi_do_translate(AMDVIAddressSpace *as, hwaddr addr,
>           return;
>       }
>   
> -    if (!amdvi_get_dte(s, devid, entry)) {
> -        return;
> -    }
> +    dte_ret = amdvi_as_to_dte(as, entry);
>   
> -    /* devices with V = 0 are not translated */
> -    if (!(entry[0] & AMDVI_DEV_VALID)) {
> +    if (dte_ret == -AMDVI_FR_DTE_V) {
> +        /* DTE[V]=0, address is passed untranslated */
>           goto out;
> +    } else if (dte_ret == -AMDVI_FR_DTE_TV) {
> +        return;
>       }
>  

Hi Alejandro,

You missed to handle -AMDVI_FR_DTE_RTR_ERR.

Regards
Sairaj Kodilkar

>       amdvi_page_walk(as, entry, ret,