From: Yu Zhang <[email protected]> Sent: Friday, August 21, 2026
6:27 AM
>
> Add page-selective IOTLB flush using HVCALL_FLUSH_DEVICE_DOMAIN_LIST.
> This hypercall accepts a list of (page_number, page_mask_shift) entries,
> enabling finer-grained IOTLB invalidation compared to the domain-wide
> HVCALL_FLUSH_DEVICE_DOMAIN used by hv_iommu_flush_iotlb_all().
>
> hv_iommu_calc_flush_range() computes the smallest power-of-two aligned
> range that covers the target IOVA region, producing a single flush
> descriptor. This may over-flush when the range is not naturally aligned,
> matching the approach used by Intel VT-d PSI. If the page-selective
> flush fails, the code falls back to a full domain flush.
>
> Signed-off-by: Easwar Hariharan <[email protected]>
> Signed-off-by: Yu Zhang <[email protected]>
> Reviewed-by: Jacob Pan <[email protected]>
> ---
> drivers/iommu/hyperv/hv-iommu-guest.c | 76 ++++++++++++++++++++++++++-
> include/hyperv/hvgdk_mini.h | 1 +
> include/hyperv/hvhdk_mini.h | 18 +++++++
> 3 files changed, 94 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/hyperv/hv-iommu-guest.c
> b/drivers/iommu/hyperv/hv-iommu-guest.c
> index 2169333020f4..3e38046bd998 100644
> --- a/drivers/iommu/hyperv/hv-iommu-guest.c
> +++ b/drivers/iommu/hyperv/hv-iommu-guest.c
> @@ -396,11 +396,84 @@ static void hv_iommu_flush_iotlb_all(struct
> iommu_domain *domain)
> hv_flush_device_domain(to_hv_iommu_domain(domain));
> }
>
> +/*
> + * Calculate the minimal power-of-two aligned range that covers [start, end]
> + * (end is inclusive). Returns a single (page_number, page_mask_shift)
> + * descriptor that may over-flush when the range is not naturally aligned.
> + */
> +static void
> +hv_iommu_calc_flush_range(unsigned long start, unsigned long end,
> + union hv_iommu_flush_va *va)
> +{
> + unsigned int sz_lg2;
> +
> + sz_lg2 = fls_long(start ^ end);
> + if (sz_lg2 < HV_HYP_PAGE_SHIFT)
> + sz_lg2 = HV_HYP_PAGE_SHIFT;
Use the max() function here instead of open coding it?
sz_lg2 = max(fls_long(start ^ end), HV_HYP_PAGE_SHIFT);
But maybe that's just more obscure. Your call.
> +
> + /*
> + * A valid IOVA range shall not span bit 63. Use the maximum mask
> + * so the host can safely perform a full flush.
> + */
> + if (WARN_ON_ONCE(sz_lg2 >= BITS_PER_LONG)) {
> + va->as_uint64 = 0;
> + va->page_mask_shift =
> + BITS_PER_LONG - HV_HYP_PAGE_SHIFT;
This case is handled slightly inconsistently with the main case.
Here the entire 64 bits are cleared, which implicitly sets the
page_number field to zero and also clears the reserved field.
The main case sets the page_number but doesn't clear the
reserved field. The memset() in hv_flush_device_domain_list()
assumes that the reserved field might not be zeroed. I'd just
suggest making everything consistent and not doing any
duplicate zero'ing.
> + return;
> + }
> +
> + va->page_number =
> + (start & GENMASK(BITS_PER_LONG - 1, sz_lg2)) >>
> + HV_HYP_PAGE_SHIFT;
> + va->page_mask_shift = sz_lg2 - HV_HYP_PAGE_SHIFT;
> +}
> +
> +static void hv_flush_device_domain_list(struct hv_iommu_domain *hv_domain,
> + struct iommu_iotlb_gather *iotlb_gather)
> +{
> + u64 status;
> + unsigned long flags;
> + struct hv_input_flush_device_domain_list *input;
> +
> + local_irq_save(flags);
> +
> + input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> + /* Clear the fixed header and the single range entry. */
> + memset(input, 0, struct_size(input, iova_list, 1));
> +
> + input->device_domain = hv_domain->device_domain;
> + input->flags |= HV_FLUSH_DEVICE_DOMAIN_LIST_IOMMU_FORMAT;
> + hv_iommu_calc_flush_range(iotlb_gather->start, iotlb_gather->end,
> + &input->iova_list[0]);
> +
> + status = hv_do_rep_hypercall(HVCALL_FLUSH_DEVICE_DOMAIN_LIST,
> + 1, 0, input, NULL);
> +
> + if (WARN_ON_ONCE(!hv_result_success(status))) {
I'd suggest having a message here with the status. The list flush really
should not be failing, so outputting the status might provide a clue
as to what's going on if it does fail.
> + /* Page-selective flush failed, fall back to full flush. */
> + struct hv_input_flush_device_domain *flush_all = (void *)input;
> +
> + memset(flush_all, 0, sizeof(*flush_all));
> + flush_all->device_domain = hv_domain->device_domain;
> + status = hv_do_hypercall(HVCALL_FLUSH_DEVICE_DOMAIN,
> + flush_all, NULL);
> + WARN(!hv_result_success(status),
> + "HVCALL_FLUSH_DEVICE_DOMAIN fallback also failed: %lld\n",
> + status);
> + }
> +
> + local_irq_restore(flags);
> +}
> +
> static void hv_iommu_iotlb_sync(struct iommu_domain *domain,
> struct iommu_iotlb_gather *iotlb_gather)
> {
> - hv_flush_device_domain(to_hv_iommu_domain(domain));
> + hv_flush_device_domain_list(to_hv_iommu_domain(domain), iotlb_gather);
>
> + /*
> + * The hypercall also invalidates non-leaf page-walk caches, so
> + * detached page-table pages can now be freed.
> + */
> iommu_put_pages_list(&iotlb_gather->freelist);
> }
>
> @@ -452,6 +525,7 @@ static struct iommu_domain
> *hv_iommu_domain_alloc_paging(struct device *dev)
>
> cfg.common.hw_max_vasz_lg2 = hv_iommu_device->max_iova_width;
> cfg.common.hw_max_oasz_lg2 = 52;
> + cfg.common.features |= BIT(PT_FEAT_FLUSH_RANGE);
> /*
> * Hyper-V S1 domains use a 4-level root for IOVA widths up to
> * 48 bits. A 5-level root is used only for wider apertures when
> diff --git a/include/hyperv/hvgdk_mini.h b/include/hyperv/hvgdk_mini.h
> index 5d1338197eee..966945f0504f 100644
> --- a/include/hyperv/hvgdk_mini.h
> +++ b/include/hyperv/hvgdk_mini.h
> @@ -497,6 +497,7 @@ union hv_vp_assist_msr_contents { /*
> HV_REGISTER_VP_ASSIST_PAGE */
> #define HVCALL_GET_GPA_PAGES_ACCESS_STATES 0x00c9
> #define HVCALL_CONFIGURE_DEVICE_DOMAIN 0x00ce
> #define HVCALL_FLUSH_DEVICE_DOMAIN 0x00d0
> +#define HVCALL_FLUSH_DEVICE_DOMAIN_LIST 0x00d1
> #define HVCALL_ACQUIRE_SPARSE_SPA_PAGE_HOST_ACCESS 0x00d7
> #define HVCALL_RELEASE_SPARSE_SPA_PAGE_HOST_ACCESS 0x00d8
> #define HVCALL_MODIFY_SPARSE_GPA_PAGE_HOST_VISIBILITY 0x00db
> diff --git a/include/hyperv/hvhdk_mini.h b/include/hyperv/hvhdk_mini.h
> index 7b9f43b320cd..57b70efe60d4 100644
> --- a/include/hyperv/hvhdk_mini.h
> +++ b/include/hyperv/hvhdk_mini.h
> @@ -685,4 +685,22 @@ struct hv_input_flush_device_domain {
> u32 reserved;
> } __packed;
>
> +union hv_iommu_flush_va { /* HV_IOMMU_GVA_RANGE */
> + u64 as_uint64;
> + struct {
> + u64 page_mask_shift : 6;
> + u64 reserved : 6;
> + u64 page_number : 52;
> + };
> +} __packed;
> +
> +/* HV_INPUT_FLUSH_DEVICE_DOMAIN_LIST */
> +struct hv_input_flush_device_domain_list {
> + struct hv_input_device_domain device_domain;
> +#define HV_FLUSH_DEVICE_DOMAIN_LIST_IOMMU_FORMAT BIT(0)
> + u32 flags;
> + u32 reserved;
> + union hv_iommu_flush_va iova_list[];
> +} __packed;
> +
> #endif /* _HV_HVHDK_MINI_H */
> --
> 2.52.0
>
