Re: [PATCH v4 17/17] KVM: arm64: Alloc simple_buffer_page using pKVM hyp allocator

On Fri, 31 Jul 2026 at 15:36, Vincent Donnefort <[email protected]> wrote:
>
> In protected mode, transition the allocation of the simple_ring_buffer
> structures from the host to the hypervisor using the new pKVM heap
> allocator.
>
> Previously, the host allocated and donated a contiguous backing memory
> for these structures. In pKVM the hypervisor can now allocate them
> dynamically.
>
> Use the pkvm_call_hyp_req() wrapper in the host to invoke
> __tracing_load, which automatically handles any top-up requests if the
> hypervisor runs out of heap memory during allocation.
>
> Tested-by: Fuad Tabba <[email protected]>
> Signed-off-by: Vincent Donnefort <[email protected]>


Reviewed-by: Fuad Tabba <[email protected]>

Cheers,
/fuad

>
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 9bab1e802281..ec5bb8541ceb 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -750,7 +750,7 @@ static void handle___tracing_load(struct kvm_cpu_context *host_ctxt)
>         DECLARE_REG(unsigned long, desc_hva, host_ctxt, 1);
>         DECLARE_REG(size_t, desc_size, host_ctxt, 2);
>
> -       cpu_reg(host_ctxt, 1) = __tracing_load(desc_hva, desc_size);
> +       errno_to_smccc(__tracing_load(desc_hva, desc_size), host_ctxt);
>  }
>
>  static void handle___tracing_unload(struct kvm_cpu_context *host_ctxt)
> diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
> index 96afa3d6de2f..5ff19d210508 100644
> --- a/arch/arm64/kvm/hyp/nvhe/trace.c
> +++ b/arch/arm64/kvm/hyp/nvhe/trace.c
> @@ -4,6 +4,7 @@
>   * Author: Vincent Donnefort <[email protected]>
>   */
>
> +#include <nvhe/alloc.h>
>  #include <nvhe/clock.h>
>  #include <nvhe/mem_protect.h>
>  #include <nvhe/mm.h>
> @@ -62,18 +63,34 @@ static void __release_host_mem(void *start, u64 size)
>         WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn(start), size >> PAGE_SHIFT));
>  }
>
> -static int hyp_trace_buffer_load_bpage_backing(struct hyp_trace_buffer *trace_buffer,
> -                                              struct hyp_trace_desc *desc)
> +static int hyp_trace_buffer_alloc_bpages(struct hyp_trace_buffer *trace_buffer,
> +                                        struct hyp_trace_desc *desc)
>  {
> -       void *start = (void *)kern_hyp_va(desc->bpages_backing_start);
> -       size_t size = desc->bpages_backing_size;
> +       void *start;
> +       size_t size;
>         int ret;
>
> -       ret = __admit_host_mem(start, size);
> -       if (ret)
> -               return ret;
> +       if (is_protected_kvm_enabled()) {
> +               struct ring_buffer_desc *rb_desc;
> +               int cpu;
>
> -       memset(start, 0, size);
> +               size = 0;
> +               for_each_ring_buffer_desc(rb_desc, cpu, &desc->trace_buffer_desc)
> +                       size += rb_desc->nr_page_va * sizeof(struct simple_buffer_page);
> +
> +               start = hyp_alloc(size);
> +               if (!start)
> +                       return hyp_alloc_errno();
> +       } else {
> +               start = (void *)kern_hyp_va(desc->bpages_backing_start);
> +               size = desc->bpages_backing_size;
> +
> +               ret = __admit_host_mem(start, size);
> +               if (ret)
> +                       return ret;
> +
> +               memset(start, 0, size);
> +       }
>
>         trace_buffer->bpages_backing_start = start;
>         trace_buffer->bpages_backing_size = size;
> @@ -81,7 +98,7 @@ static int hyp_trace_buffer_load_bpage_backing(struct hyp_trace_buffer *trace_bu
>         return 0;
>  }
>
> -static void hyp_trace_buffer_unload_bpage_backing(struct hyp_trace_buffer *trace_buffer)
> +static void hyp_trace_buffer_free_bpages(struct hyp_trace_buffer *trace_buffer)
>  {
>         void *start = trace_buffer->bpages_backing_start;
>         size_t size = trace_buffer->bpages_backing_size;
> @@ -89,9 +106,12 @@ static void hyp_trace_buffer_unload_bpage_backing(struct hyp_trace_buffer *trace
>         if (!size)
>                 return;
>
> -       memset(start, 0, size);
> -
> -       __release_host_mem(start, size);
> +       if (is_protected_kvm_enabled()) {
> +               hyp_free(start);
> +       } else {
> +               memset(start, 0, size);
> +               __release_host_mem(start, size);
> +       }
>
>         trace_buffer->bpages_backing_start = 0;
>         trace_buffer->bpages_backing_size = 0;
> @@ -128,7 +148,7 @@ static void hyp_trace_buffer_unload(struct hyp_trace_buffer *trace_buffer)
>                 simple_ring_buffer_unload_mm(per_cpu_ptr(trace_buffer->simple_rbs, cpu),
>                                              __unpin_shared_page);
>
> -       hyp_trace_buffer_unload_bpage_backing(trace_buffer);
> +       hyp_trace_buffer_free_bpages(trace_buffer);
>  }
>
>  static int hyp_trace_buffer_load(struct hyp_trace_buffer *trace_buffer,
> @@ -143,7 +163,7 @@ static int hyp_trace_buffer_load(struct hyp_trace_buffer *trace_buffer,
>         if (hyp_trace_buffer_loaded(trace_buffer))
>                 return -EINVAL;
>
> -       ret = hyp_trace_buffer_load_bpage_backing(trace_buffer, desc);
> +       ret = hyp_trace_buffer_alloc_bpages(trace_buffer, desc);
>         if (ret)
>                 return ret;
>
> @@ -168,18 +188,16 @@ static bool hyp_trace_desc_is_valid(struct hyp_trace_desc *desc, size_t desc_siz
>  {
>         struct ring_buffer_desc *rb_desc;
>         unsigned int cpu;
> -       size_t nr_bpages;
>         void *desc_end;
>
>         if (!is_protected_kvm_enabled())
>                 return true;
>
>         /*
> -        * Both desc_size and bpages_backing_size are untrusted host-provided
> -        * values. We rely on __pkvm_host_donate_hyp() to enforce their validity.
> +        * desc_size is an untrusted host-provided value. We rely on
> +        * __pkvm_host_donate_hyp() to enforce its validity.
>          */
>         desc_end = (void *)desc + desc_size;
> -       nr_bpages = desc->bpages_backing_size / sizeof(struct simple_buffer_page);
>
>         if (desc->trace_buffer_desc.nr_cpus != hyp_nr_cpus)
>                 return false;
> @@ -197,17 +215,8 @@ static bool hyp_trace_desc_is_valid(struct hyp_trace_desc *desc, size_t desc_siz
>                 if ((void *)rb_desc + struct_size(rb_desc, page_va, rb_desc->nr_page_va) > desc_end)
>                         return false;
>
> -               /* Overflow bpages backing memory? */
> -               if (nr_bpages < rb_desc->nr_page_va)
> -                       return false;
> -
> -               if (cpu >= hyp_nr_cpus)
> -                       return false;
> -
>                 if (cpu != rb_desc->cpu)
>                         return false;
> -
> -               nr_bpages -= rb_desc->nr_page_va;
>         }
>
>         return true;
> diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
> index 2411b4c32932..859a926c815f 100644
> --- a/arch/arm64/kvm/hyp_trace.c
> +++ b/arch/arm64/kvm/hyp_trace.c
> @@ -13,6 +13,7 @@
>  #include <asm/kvm_host.h>
>  #include <asm/kvm_hyptrace.h>
>  #include <asm/kvm_mmu.h>
> +#include <asm/kvm_pkvm.h>
>
>  #include "hyp_trace.h"
>
> @@ -157,10 +158,17 @@ static void __unshare_page(unsigned long va)
>
>  static int hyp_trace_buffer_alloc_bpages_backing(struct hyp_trace_buffer *trace_buffer, size_t size)
>  {
> -       int nr_bpages = (PAGE_ALIGN(size) / PAGE_SIZE) + 1;
>         size_t backing_size;
> +       int nr_bpages;
>         void *start;
>
> +       if (is_protected_kvm_enabled()) {
> +               trace_buffer->desc->bpages_backing_start = 0;
> +               trace_buffer->desc->bpages_backing_size = 0;
> +               return 0;
> +       }
> +
> +       nr_bpages = (PAGE_ALIGN(size) / PAGE_SIZE) + 1;
>         backing_size = PAGE_ALIGN(sizeof(struct simple_buffer_page) * nr_bpages *
>                                   num_possible_cpus());
>
> @@ -176,6 +184,9 @@ static int hyp_trace_buffer_alloc_bpages_backing(struct hyp_trace_buffer *trace_
>
>  static void hyp_trace_buffer_free_bpages_backing(struct hyp_trace_buffer *trace_buffer)
>  {
> +       if (!trace_buffer->desc->bpages_backing_start)
> +               return;
> +
>         free_pages_exact((void *)trace_buffer->desc->bpages_backing_start,
>                          trace_buffer->desc->bpages_backing_size);
>  }
> @@ -264,7 +275,7 @@ static struct trace_buffer_desc *hyp_trace_load(unsigned long size, void *priv)
>         if (ret)
>                 goto err_free_buffer;
>
> -       ret = kvm_call_hyp_nvhe(__tracing_load, (unsigned long)desc, desc_size);
> +       ret = pkvm_call_hyp_req(__tracing_load, (unsigned long)desc, desc_size);
>         if (ret)
>                 goto err_unload_pages;
>
> --
> 2.55.0.508.g3f0d502094-goog
>