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SubjectRe: [RFC v2 12/20] dma-iommu: Implement NESTED_MSI cookie
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Hi Eric,

On 2018-09-18 3:24 pm, Eric Auger wrote:
> Up to now, when the type was UNMANAGED, we used to
> allocate IOVA pages within a range provided by the user.
> This does not work in nested mode.
>
> If both the host and the guest are exposed with SMMUs, each
> would allocate an IOVA. The guest allocates an IOVA (gIOVA)
> to map onto the guest MSI doorbell (gDB). The Host allocates
> another IOVA (hIOVA) to map onto the physical doorbell (hDB).
>
> So we end up with 2 unrelated mappings, at S1 and S2:
> S1 S2
> gIOVA -> gDB
> hIOVA -> hDB
>
> The PCI device would be programmed with hIOVA.
>
> iommu_dma_bind_doorbell allows to pass gIOVA/gDB to the host
> so that gIOVA can be used by the host instead of re-allocating
> a new IOVA. That way the host can create the following nested
> mapping:
>
> S1 S2
> gIOVA -> gDB -> hDB
>
> this time, the PCI device will be programmed with the gIOVA MSI
> doorbell which is correctly map through the 2 stages.

If I'm understanding things correctly, this plus a couple of the
preceding patches all add up to a rather involved way of coercing an
automatic allocator to only "allocate" predetermined addresses in an
entirely known-ahead-of-time manner. Given that the guy calling
iommu_dma_bind_doorbell() could seemingly just as easily call
iommu_map() at that point and not bother with an allocator cookie and
all this machinery at all, what am I missing?

Robin.

>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
>
> v1 -> v2:
> - unmap stage2 on put()
> ---
> drivers/iommu/dma-iommu.c | 97 +++++++++++++++++++++++++++++++++++++--
> include/linux/dma-iommu.h | 11 +++++
> 2 files changed, 105 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 511ff9a1d6d9..53444c3e8f2f 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -37,12 +37,14 @@
> struct iommu_dma_msi_page {
> struct list_head list;
> dma_addr_t iova;
> + dma_addr_t ipa;
> phys_addr_t phys;
> };
>
> enum iommu_dma_cookie_type {
> IOMMU_DMA_IOVA_COOKIE,
> IOMMU_DMA_MSI_COOKIE,
> + IOMMU_DMA_NESTED_MSI_COOKIE,
> };
>
> struct iommu_dma_cookie {
> @@ -109,14 +111,17 @@ EXPORT_SYMBOL(iommu_get_dma_cookie);
> *
> * Users who manage their own IOVA allocation and do not want DMA API support,
> * but would still like to take advantage of automatic MSI remapping, can use
> - * this to initialise their own domain appropriately. Users should reserve a
> + * this to initialise their own domain appropriately. Users may reserve a
> * contiguous IOVA region, starting at @base, large enough to accommodate the
> * number of PAGE_SIZE mappings necessary to cover every MSI doorbell address
> - * used by the devices attached to @domain.
> + * used by the devices attached to @domain. The other way round is to provide
> + * usable iova pages through the iommu_dma_bind_doorbell API (nested stages
> + * use case)
> */
> int iommu_get_msi_cookie(struct iommu_domain *domain, dma_addr_t base)
> {
> struct iommu_dma_cookie *cookie;
> + int nesting, ret;
>
> if (domain->type != IOMMU_DOMAIN_UNMANAGED)
> return -EINVAL;
> @@ -124,7 +129,12 @@ int iommu_get_msi_cookie(struct iommu_domain *domain, dma_addr_t base)
> if (domain->iova_cookie)
> return -EEXIST;
>
> - cookie = cookie_alloc(IOMMU_DMA_MSI_COOKIE);
> + ret = iommu_domain_get_attr(domain, DOMAIN_ATTR_NESTING, &nesting);
> + if (!ret && nesting)
> + cookie = cookie_alloc(IOMMU_DMA_NESTED_MSI_COOKIE);
> + else
> + cookie = cookie_alloc(IOMMU_DMA_MSI_COOKIE);
> +
> if (!cookie)
> return -ENOMEM;
>
> @@ -145,6 +155,7 @@ void iommu_put_dma_cookie(struct iommu_domain *domain)
> {
> struct iommu_dma_cookie *cookie = domain->iova_cookie;
> struct iommu_dma_msi_page *msi, *tmp;
> + bool s2_unmap = false;
>
> if (!cookie)
> return;
> @@ -152,7 +163,15 @@ void iommu_put_dma_cookie(struct iommu_domain *domain)
> if (cookie->type == IOMMU_DMA_IOVA_COOKIE && cookie->iovad.granule)
> put_iova_domain(&cookie->iovad);
>
> + if (cookie->type == IOMMU_DMA_NESTED_MSI_COOKIE)
> + s2_unmap = true;
> +
> list_for_each_entry_safe(msi, tmp, &cookie->msi_page_list, list) {
> + if (s2_unmap && msi->phys) {
> + size_t size = cookie_msi_granule(cookie);
> +
> + WARN_ON(iommu_unmap(domain, msi->ipa, size) != size);
> + }
> list_del(&msi->list);
> kfree(msi);
> }
> @@ -161,6 +180,50 @@ void iommu_put_dma_cookie(struct iommu_domain *domain)
> }
> EXPORT_SYMBOL(iommu_put_dma_cookie);
>
> +/**
> + * iommu_dma_bind_doorbell - Allows to provide a usable IOVA page
> + * @domain: domain handle
> + * @binding: IOVA/IPA binding
> + *
> + * In nested stage use case, the user can provide IOVA/IPA bindings
> + * corresponding to a guest MSI stage 1 mapping. When the host needs
> + * to map its own MSI doorbells, it can use the IPA as stage 2 input
> + * and map it onto the physical MSI doorbell.
> + */
> +int iommu_dma_bind_doorbell(struct iommu_domain *domain,
> + struct iommu_guest_msi_binding *binding)
> +{
> + struct iommu_dma_cookie *cookie = domain->iova_cookie;
> + struct iommu_dma_msi_page *msi;
> + dma_addr_t ipa, iova;
> + size_t size;
> +
> + if (!cookie)
> + return -EINVAL;
> +
> + if (cookie->type != IOMMU_DMA_NESTED_MSI_COOKIE)
> + return -EINVAL;
> +
> + size = 1 << binding->granule;
> + iova = binding->iova & ~(phys_addr_t)(size - 1);
> + ipa = binding->gpa & ~(phys_addr_t)(size - 1);
> +
> + list_for_each_entry(msi, &cookie->msi_page_list, list) {
> + if (msi->iova == iova)
> + return 0; /* this page is already registered */
> + }
> +
> + msi = kzalloc(sizeof(*msi), GFP_KERNEL);
> + if (!msi)
> + return -ENOMEM;
> +
> + msi->iova = iova;
> + msi->ipa = ipa;
> + list_add(&msi->list, &cookie->msi_page_list);
> + return 0;
> +}
> +EXPORT_SYMBOL(iommu_dma_bind_doorbell);
> +
> /**
> * iommu_dma_get_resv_regions - Reserved region driver helper
> * @dev: Device from iommu_get_resv_regions()
> @@ -846,6 +909,34 @@ static struct iommu_dma_msi_page *iommu_dma_get_msi_page(struct device *dev,
> if (msi_page->phys == msi_addr)
> return msi_page;
>
> + /*
> + * In nested stage mode, we do not allocate an MSI page in
> + * a range provided by the user. Instead, IOVA/IPA bindings are
> + * individually provided. We reuse thise IOVAs to build the
> + * IOVA -> IPA -> MSI PA nested stage mapping.
> + */
> + if (cookie->type == IOMMU_DMA_NESTED_MSI_COOKIE) {
> + list_for_each_entry(msi_page, &cookie->msi_page_list, list)
> + if (!msi_page->phys) { /* this binding is free to use */
> + dma_addr_t ipa = msi_page->ipa;
> + int ret;
> +
> + msi_page->phys = msi_addr;
> +
> + /* do the stage 2 mapping */
> + ret = iommu_map(domain, ipa, msi_addr, size,
> + IOMMU_MMIO | IOMMU_WRITE);
> + if (ret) {
> + pr_warn("MSI S2 mapping failed (%d)\n",
> + ret);
> + return NULL;
> + }
> + return msi_page;
> + }
> + pr_warn("%s no MSI binding found\n", __func__);
> + return NULL;
> + }
> +
> msi_page = kzalloc(sizeof(*msi_page), GFP_ATOMIC);
> if (!msi_page)
> return NULL;
> diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
> index e8ca5e654277..324745eef644 100644
> --- a/include/linux/dma-iommu.h
> +++ b/include/linux/dma-iommu.h
> @@ -24,6 +24,7 @@
> #include <linux/dma-mapping.h>
> #include <linux/iommu.h>
> #include <linux/msi.h>
> +#include <uapi/linux/iommu.h>
>
> int iommu_dma_init(void);
>
> @@ -74,12 +75,15 @@ int iommu_dma_mapping_error(struct device *dev, dma_addr_t dma_addr);
> /* The DMA API isn't _quite_ the whole story, though... */
> void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg);
> void iommu_dma_get_resv_regions(struct device *dev, struct list_head *list);
> +int iommu_dma_bind_doorbell(struct iommu_domain *domain,
> + struct iommu_guest_msi_binding *binding);
>
> #else
>
> struct iommu_domain;
> struct msi_msg;
> struct device;
> +struct iommu_guest_msi_binding;
>
> static inline int iommu_dma_init(void)
> {
> @@ -104,6 +108,13 @@ static inline void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg)
> {
> }
>
> +static inline int
> +iommu_dma_bind_doorbell(struct iommu_domain *domain,
> + struct iommu_guest_msi_binding *binding)
> +{
> + return -ENODEV;
> +}
> +
> static inline void iommu_dma_get_resv_regions(struct device *dev, struct list_head *list)
> {
> }
>

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