[PATCH 17/17] KVM: arm64: Alloc simple_buffer_page using pKVM hyp allocator
Vincent Donnefort
vdonnefort at google.com
Wed May 20 08:26:50 PDT 2026
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.
Signed-off-by: Vincent Donnefort <vdonnefort at google.com>
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 8d7e44e657eb..376bf0fd2a2d 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -725,7 +725,7 @@ 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 a6ca27b18e15..680fe1cdf4a2 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -4,6 +4,7 @@
* Author: Vincent Donnefort <vdonnefort at google.com>
*/
+#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;
+
+ 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;
- memset(start, 0, 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;
@@ -164,19 +184,20 @@ static int hyp_trace_buffer_load(struct hyp_trace_buffer *trace_buffer,
return ret;
}
-static bool hyp_trace_desc_validate(struct hyp_trace_desc *desc, size_t desc_size)
+static bool hyp_trace_desc_is_valid(struct hyp_trace_desc *desc, size_t desc_size)
{
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);
for_each_ring_buffer_desc(rb_desc, cpu, &desc->trace_buffer_desc) {
/* Can we read nr_page_va? */
@@ -187,17 +208,11 @@ static bool hyp_trace_desc_validate(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;
@@ -212,8 +227,10 @@ int __tracing_load(unsigned long desc_hva, size_t desc_size)
if (ret)
return ret;
- if (!hyp_trace_desc_validate(desc, desc_size))
+ if (!hyp_trace_desc_is_valid(desc, desc_size)) {
+ ret = -EINVAL;
goto err_release_desc;
+ }
hyp_spin_lock(&trace_buffer.lock);
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index 8b7f2bf2fba8..afc8c3ea68f5 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 +158,18 @@ 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;
+ /* pKVM uses hyp_alloc() to allocate struct simple_buffer_page */
+ 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 +185,9 @@ 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);
}
@@ -262,7 +274,7 @@ 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;
--
2.54.0.631.ge1b05301d1-goog
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