[PATCH v6 09/25] KVM: arm64: iommu: Add memory pool
Vincent Donnefort
vdonnefort at google.com
Fri Jul 10 09:33:14 PDT 2026
On Fri, May 01, 2026 at 11:19:11AM +0000, Mostafa Saleh wrote:
> IOMMU drivers would require to allocate memory for the shadow page
> table. Similar to the host stage-2 CPU page table, the IOMMU pool
> is allocated early from the carveout and it's memory is added in
> a pool which the IOMMU driver can allocate from and reclaim at
> run time.
>
> As this is too early for drivers to use init calls, set the number of
> page allocated from the kernel command line "kvm-arm.hyp_iommu_pages".
>
> Later when the driver registers, it will pass how many pages it
> needs, and if it was less than what was allocated, it will fail
> to register.
>
> Signed-off-by: Mostafa Saleh <smostafa at google.com>
> ---
> .../admin-guide/kernel-parameters.txt | 4 +++
> arch/arm64/include/asm/kvm_host.h | 3 +-
> arch/arm64/kvm/hyp/include/nvhe/iommu.h | 7 +++-
> arch/arm64/kvm/hyp/nvhe/iommu/iommu.c | 21 +++++++++++-
> arch/arm64/kvm/hyp/nvhe/setup.c | 12 ++++++-
> arch/arm64/kvm/iommu.c | 33 ++++++++++++++++++-
> arch/arm64/kvm/pkvm.c | 1 +
> 7 files changed, 76 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index cf3807641d89..5e49946ff7ed 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3283,6 +3283,10 @@ Kernel parameters
> trap: set WFI instruction trap
>
> notrap: clear WFI instruction trap
> + kvm-arm.hyp_iommu_pages=
> + [KVM, ARM, EARLY]
> + Number of pages allocated for the IOMMU pool from the
> + KVM carveout when running in protected mode.
>
> kvm_cma_resv_ratio=n [PPC,EARLY]
> Reserves given percentage from system memory area for
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 52898d2a3ec6..17f4cce86ec3 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1735,7 +1735,8 @@ long kvm_get_cap_for_kvm_ioctl(unsigned int ioctl, long *ext);
>
> #ifndef __KVM_NVHE_HYPERVISOR__
> struct kvm_iommu_ops;
> -int kvm_iommu_register_driver(struct kvm_iommu_ops *hyp_ops);
> +int kvm_iommu_register_driver(struct kvm_iommu_ops *hyp_ops, unsigned int pool_pages);
> +unsigned int kvm_iommu_pages(void);
> #endif
>
> #endif /* __ARM64_KVM_HOST_H__ */
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/iommu.h b/arch/arm64/kvm/hyp/include/nvhe/iommu.h
> index 6277d845cdcf..eba94b4f6050 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/iommu.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/iommu.h
> @@ -10,8 +10,13 @@ struct kvm_iommu_ops {
> int (*host_stage2_idmap)(phys_addr_t start, phys_addr_t end, int prot);
> };
>
> -int kvm_iommu_init(void);
> +int kvm_iommu_init(void *pool_base, unsigned int nr_pages);
>
> int kvm_iommu_host_stage2_idmap(phys_addr_t start, phys_addr_t end,
> enum kvm_pgtable_prot prot);
> +
> +/* Returns zeroed memory. */
If we expect drivers to use that perhaps we should document a bit better (same
for kvm_iommu_reclaim_pages()
> +void *kvm_iommu_donate_pages(u8 order);
> +void kvm_iommu_reclaim_pages(void *ptr);
> +
> #endif /* __ARM64_KVM_NVHE_IOMMU_H__ */
> diff --git a/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c b/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
> index 1db52bd87c38..53cb5e4b0aac 100644
> --- a/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
> +++ b/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
Do we really need that subfolder iommu/ ?
> @@ -15,6 +15,7 @@ struct kvm_iommu_ops *kvm_iommu_ops;
>
> /* Protected by host_mmu.lock */
> static bool kvm_idmap_initialized;
> +static struct hyp_pool iommu_pages_pool;
>
> static inline int pkvm_to_iommu_prot(enum kvm_pgtable_prot prot)
> {
> @@ -95,7 +96,7 @@ static int kvm_iommu_snapshot_host_stage2(void)
> return ret;
> }
>
> -int kvm_iommu_init(void)
> +int kvm_iommu_init(void *pool_base, unsigned int nr_pages)
> {
> int ret;
>
> @@ -103,6 +104,14 @@ int kvm_iommu_init(void)
> !kvm_iommu_ops->host_stage2_idmap)
> return 0;
>
> + if (!nr_pages)
> + return -ENOMEM;
> +
> + ret = hyp_pool_init(&iommu_pages_pool, hyp_virt_to_pfn(pool_base),
> + nr_pages, 0);
> + if (ret)
> + return ret;
> +
> ret = kvm_iommu_ops->init();
> if (ret)
> return ret;
> @@ -120,3 +129,13 @@ int kvm_iommu_host_stage2_idmap(phys_addr_t start, phys_addr_t end,
>
> return kvm_iommu_ops->host_stage2_idmap(start, end, pkvm_to_iommu_prot(prot));
> }
> +
> +void *kvm_iommu_donate_pages(u8 order)
> +{
> + return hyp_alloc_pages(&iommu_pages_pool, order);
> +}
> +
> +void kvm_iommu_reclaim_pages(void *ptr)
> +{
> + hyp_put_page(&iommu_pages_pool, ptr);
> +}
> diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
> index 1f6b221db9a0..215014e42c27 100644
> --- a/arch/arm64/kvm/hyp/nvhe/setup.c
> +++ b/arch/arm64/kvm/hyp/nvhe/setup.c
> @@ -23,6 +23,9 @@
>
> unsigned long hyp_nr_cpus;
>
> +/* See kvm_iommu_pages() */
> +unsigned int hyp_kvm_iommu_pages;
nit: we tend to use everywhere unsigned long or u64 for nr_pages.
> +
> #define hyp_percpu_size ((unsigned long)__per_cpu_end - \
> (unsigned long)__per_cpu_start)
>
> @@ -34,6 +37,7 @@ static void *selftest_base;
> static void *ffa_proxy_pages;
> static struct kvm_pgtable_mm_ops pkvm_pgtable_mm_ops;
> static struct hyp_pool hpool;
> +static void *iommu_base;
>
> static int divide_memory_pool(void *virt, unsigned long size)
> {
> @@ -71,6 +75,12 @@ static int divide_memory_pool(void *virt, unsigned long size)
> if (!ffa_proxy_pages)
> return -ENOMEM;
>
> + if (hyp_kvm_iommu_pages) {
> + iommu_base = hyp_early_alloc_contig(hyp_kvm_iommu_pages);
> + if (!iommu_base)
> + return -ENOMEM;
> + }
> +
> return 0;
> }
>
> @@ -330,7 +340,7 @@ void __noreturn __pkvm_init_finalise(void)
> if (ret)
> goto out;
>
> - ret = kvm_iommu_init();
> + ret = kvm_iommu_init(iommu_base, hyp_kvm_iommu_pages);
> if (ret)
> goto out;
>
> diff --git a/arch/arm64/kvm/iommu.c b/arch/arm64/kvm/iommu.c
> index f247384fa193..213429ceb549 100644
> --- a/arch/arm64/kvm/iommu.c
> +++ b/arch/arm64/kvm/iommu.c
> @@ -7,10 +7,11 @@
> #include <linux/kvm_host.h>
>
> extern struct kvm_iommu_ops *kvm_nvhe_sym(kvm_iommu_ops);
> +extern unsigned int kvm_nvhe_sym(hyp_kvm_iommu_pages);
>
> static DEFINE_MUTEX(kvm_iommu_reg_lock);
>
> -int kvm_iommu_register_driver(struct kvm_iommu_ops *hyp_ops)
> +int kvm_iommu_register_driver(struct kvm_iommu_ops *hyp_ops, unsigned int pool_pages)
nit: kvm_iommu_init uses nr_pages.
> {
> guard(mutex)(&kvm_iommu_reg_lock);
>
> @@ -21,6 +22,36 @@ int kvm_iommu_register_driver(struct kvm_iommu_ops *hyp_ops)
> if (kvm_nvhe_sym(kvm_iommu_ops))
> return -EBUSY;
>
> + /* See kvm_iommu_pages() */
> + if (pool_pages > kvm_nvhe_sym(hyp_kvm_iommu_pages)) {
> + kvm_err("Not enough memory for the IOMMU pool, need 0x%x pages, check kvm-arm.hyp_iommu_pages",
> + pool_pages);
> + return -ENOMEM;
> + }
> +
> kvm_nvhe_sym(kvm_iommu_ops) = hyp_ops;
> return 0;
> }
> +
> +unsigned int kvm_iommu_pages(void)
> +{
> + /*
> + * This is used very early during setup_arch() before any initcalls
> + * or any drivers are registered.
> + * This value is set by a command line option.
> + * Later, when the driver is registered, it will pass the number
> + * pages needed for it's page tables, if it was less that what
> + * the system has already allocated, the registration will fail.
> + */
> + return kvm_nvhe_sym(hyp_kvm_iommu_pages);
> +}
Could we actually estimate the memory needed, based on the allocation for the
host stage-2 and an estimation of MMIO coverage? This would allow the whole
thing to run without setting this value as a best effort and to make it
optional, which is surely more user-friendly?
> +
> +/* Number of pages to reserve for iommu pool*/
> +static int __init early_hyp_iommu_pages(char *arg)
> +{
> + if (!arg)
> + return -EINVAL;
> +
> + return kstrtouint(arg, 0, &kvm_nvhe_sym(hyp_kvm_iommu_pages));
How about using a memory size here with memparse()? This would be more
transparent for the commandline which can work on different page-size systems.
> +}
> +early_param("kvm-arm.hyp_iommu_pages", early_hyp_iommu_pages);
> diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
> index 053e4f733e4b..79dd14db4919 100644
> --- a/arch/arm64/kvm/pkvm.c
> +++ b/arch/arm64/kvm/pkvm.c
> @@ -63,6 +63,7 @@ void __init kvm_hyp_reserve(void)
> hyp_mem_pages += hyp_vmemmap_pages(STRUCT_HYP_PAGE_SIZE);
> hyp_mem_pages += pkvm_selftest_pages();
> hyp_mem_pages += hyp_ffa_proxy_pages();
> + hyp_mem_pages += kvm_iommu_pages();
>
> /*
> * Try to allocate a PMD-aligned region to reduce TLB pressure once
> --
> 2.54.0.545.g6539524ca2-goog
>
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