Re: [RFC PATCH 15/45] KVM: arm64: pkvm: Add __pkvm_host_share/unshare_dma()

tina.zhang
2023-02-04T12:53:25Z

On 2/1/23 20:52, Jean-Philippe Brucker wrote:
> Host pages mapped in the SMMU must not be donated to the guest or
> hypervisor, since the host could then use DMA to break confidentiality.
> Mark them shared in the host stage-2 page tables, and keep a refcount in
> the hyp vmemmap.
>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
> arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 3 +
> arch/arm64/kvm/hyp/nvhe/mem_protect.c | 185 ++++++++++++++++++
> 2 files changed, 188 insertions(+)
>
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> index 021825aee854..a363d58a998b 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> @@ -58,6 +58,7 @@ enum pkvm_component_id {
> PKVM_ID_HOST,
> PKVM_ID_HYP,
> PKVM_ID_GUEST,
> + PKVM_ID_IOMMU,
> };
>
> extern unsigned long hyp_nr_cpus;
> @@ -72,6 +73,8 @@ int __pkvm_host_share_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu);
> int __pkvm_host_donate_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu);
> int __pkvm_guest_share_host(struct pkvm_hyp_vcpu *hyp_vcpu, u64 ipa);
> int __pkvm_guest_unshare_host(struct pkvm_hyp_vcpu *hyp_vcpu, u64 ipa);
> +int __pkvm_host_share_dma(u64 phys_addr, size_t size, bool is_ram);
> +int __pkvm_host_unshare_dma(u64 phys_addr, size_t size);
>
> bool addr_is_memory(phys_addr_t phys);
> int host_stage2_idmap_locked(phys_addr_t addr, u64 size, enum kvm_pgtable_prot prot);
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index 856673291d70..dcf08ce03790 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -1148,6 +1148,9 @@ static int check_share(struct pkvm_mem_share *share)
> case PKVM_ID_GUEST:
> ret = guest_ack_share(completer_addr, tx, share->completer_prot);
> break;
> + case PKVM_ID_IOMMU:
> + ret = 0;
> + break;
> default:
> ret = -EINVAL;
> }
> @@ -1185,6 +1188,9 @@ static int __do_share(struct pkvm_mem_share *share)
> case PKVM_ID_GUEST:
> ret = guest_complete_share(completer_addr, tx, share->completer_prot);
> break;
> + case PKVM_ID_IOMMU:
> + ret = 0;
> + break;
> default:
> ret = -EINVAL;
> }
> @@ -1239,6 +1245,9 @@ static int check_unshare(struct pkvm_mem_share *share)
> case PKVM_ID_HYP:
> ret = hyp_ack_unshare(completer_addr, tx);
> break;
> + case PKVM_ID_IOMMU:
> + ret = 0;
> + break;
> default:
> ret = -EINVAL;
> }
> @@ -1273,6 +1282,9 @@ static int __do_unshare(struct pkvm_mem_share *share)
> case PKVM_ID_HYP:
> ret = hyp_complete_unshare(completer_addr, tx);
> break;
> + case PKVM_ID_IOMMU:
> + ret = 0;
> + break;
> default:
> ret = -EINVAL;
> }
> @@ -1633,6 +1645,179 @@ void hyp_unpin_shared_mem(void *from, void *to)
> host_unlock_component();
> }
>
> +static int __host_check_page_dma_shared(phys_addr_t phys_addr)
> +{
> + int ret;
> + u64 hyp_addr;
> +
> + /*
> + * The page is already refcounted. Make sure it's owned by the host, and
> + * not part of the hyp pool.
> + */
> + ret = __host_check_page_state_range(phys_addr, PAGE_SIZE,
> + PKVM_PAGE_SHARED_OWNED);
> + if (ret)
> + return ret;
> +
> + /*
> + * Refcounted and owned by host, means it's either mapped in the
> + * SMMU, or it's some VM/VCPU state shared with the hypervisor.
> + * The host has no reason to use a page for both.
> + */
> + hyp_addr = (u64)hyp_phys_to_virt(phys_addr);
> + return __hyp_check_page_state_range(hyp_addr, PAGE_SIZE, PKVM_NOPAGE);
> +}
> +
> +static int __pkvm_host_share_dma_page(phys_addr_t phys_addr, bool is_ram)
> +{
> + int ret;
> + struct hyp_page *p = hyp_phys_to_page(phys_addr);
> + struct pkvm_mem_share share = {
> + .tx = {
> + .nr_pages = 1,
> + .initiator = {
> + .id = PKVM_ID_HOST,
> + .addr = phys_addr,
> + },
> + .completer = {
> + .id = PKVM_ID_IOMMU,
> + },
> + },
> + };
> +
> + hyp_assert_lock_held(&host_mmu.lock);
> + hyp_assert_lock_held(&pkvm_pgd_lock);
> +
> + /*
> + * Some differences between handling of RAM and device memory:
> + * - The hyp vmemmap area for device memory is not backed by physical
> + * pages in the hyp page tables.
> + * - Device memory is unmapped automatically under memory pressure
> + * (host_stage2_try()) and the ownership information would be
> + * discarded.
> + * We don't need to deal with that at the moment, because the host
> + * cannot share or donate device memory, only RAM.
> + *
> + * Since 'is_ram' is only a hint provided by the host, we do need to
> + * make sure of it.
> + */
> + if (!is_ram)
> + return addr_is_memory(phys_addr) ? -EINVAL : 0;
> +
> + ret = hyp_page_ref_inc_return(p);
> + BUG_ON(ret == 0);
> + if (ret < 0)
> + return ret;
> + else if (ret == 1)
> + ret = do_share(&share);
> + else
> + ret = __host_check_page_dma_shared(phys_addr);
> +
> + if (ret)
> + hyp_page_ref_dec(p);
> +
> + return ret;
> +}
> +
> +static int __pkvm_host_unshare_dma_page(phys_addr_t phys_addr)
> +{
> + struct hyp_page *p = hyp_phys_to_page(phys_addr);
> + struct pkvm_mem_share share = {
> + .tx = {
> + .nr_pages = 1,
> + .initiator = {
> + .id = PKVM_ID_HOST,
> + .addr = phys_addr,
> + },
> + .completer = {
> + .id = PKVM_ID_IOMMU,
> + },
> + },
> + };
> +
> + hyp_assert_lock_held(&host_mmu.lock);
> + hyp_assert_lock_held(&pkvm_pgd_lock);
> +
> + if (!addr_is_memory(phys_addr))
> + return 0;
> +
> + if (!hyp_page_ref_dec_and_test(p))
> + return 0;
> +
> + return do_unshare(&share);
> +}
> +
> +/*
> + * __pkvm_host_share_dma - Mark host memory as used for DMA
> + * @phys_addr: physical address of the DMA region
> + * @size: size of the DMA region
> + * @is_ram: whether it is RAM or device memory
> + *
> + * We must not allow the host to donate pages that are mapped in the IOMMU for
> + * DMA. So:
> + * 1. Mark the host S2 entry as being owned by IOMMU
> + * 2. Refcount it, since a page may be mapped in multiple device address spaces.
> + *
> + * At some point we may end up needing more than the current 16 bits for
> + * refcounting, for example if all devices and sub-devices map the same MSI
> + * doorbell page. It will do for now.
> + */
> +int __pkvm_host_share_dma(phys_addr_t phys_addr, size_t size, bool is_ram)
> +{
> + int i;
> + int ret;
> + size_t nr_pages = size >> PAGE_SHIFT;
> +
> + if (WARN_ON(!PAGE_ALIGNED(phys_addr | size)))
> + return -EINVAL;
> +
> + host_lock_component();
> + hyp_lock_component();
> +
> + for (i = 0; i < nr_pages; i++) {
> + ret = __pkvm_host_share_dma_page(phys_addr + i * PAGE_SIZE,
> + is_ram);
Hi Jean,

I'm not familiar with ARM arch. Just out of curiosity. If pKVM-ARM
populates the host stage-2 page table lazily, would there be a case that
device driver in host triggers DMA with pages which have not been mapped
to the host stage-2 page table yet? How do we handle this situation?

Regards,
-Tina

> + if (ret)
> + break;
> + }
> +
> + if (ret) {
> + for (--i; i >= 0; --i)
> + __pkvm_host_unshare_dma_page(phys_addr + i * PAGE_SIZE);
> + }
> +
> + hyp_unlock_component();
> + host_unlock_component();
> +
> + return ret;
> +}
> +
> +int __pkvm_host_unshare_dma(phys_addr_t phys_addr, size_t size)
> +{
> + int i;
> + int ret;
> + size_t nr_pages = size >> PAGE_SHIFT;
> +
> + host_lock_component();
> + hyp_lock_component();
> +
> + /*
> + * We end up here after the caller successfully unmapped the page from
> + * the IOMMU table. Which means that a ref is held, the page is shared
> + * in the host s2, there can be no failure.
> + */
> + for (i = 0; i < nr_pages; i++) {
> + ret = __pkvm_host_unshare_dma_page(phys_addr + i * PAGE_SIZE);
> + if (ret)
> + break;
> + }
> +
> + hyp_unlock_component();
> + host_unlock_component();
> +
> + return ret;
> +}
> +
> int __pkvm_host_share_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu)
> {
> int ret;