RE: [PATCH v5 06/16] x86/hyperv: allocate output arg pages if required

When Linux runs as the root partition, it will need to make hypercalls
which return data from the hypervisor.

Allocate pages for storing results when Linux runs as the root
partition.

Signed-off-by: Lillian Grassin-Drake <redacted>
Co-Developed-by: Lillian Grassin-Drake <redacted>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
---
v3: Fix hv_cpu_die to use free_pages.
v2: Address Vitaly's comments
---
 arch/x86/hyperv/hv_init.c       | 35 ++++++++++++++++++++++++++++-----
 arch/x86/include/asm/mshyperv.h |  1 +
 2 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index e04d90af4c27..6f4cb40e53fe 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c

@@ -41,6 +41,9 @@ EXPORT_SYMBOL_GPL(hv_vp_assist_page);
 void  __percpu **hyperv_pcpu_input_arg;
 EXPORT_SYMBOL_GPL(hyperv_pcpu_input_arg);

+void  __percpu **hyperv_pcpu_output_arg;
+EXPORT_SYMBOL_GPL(hyperv_pcpu_output_arg);
+
 u32 hv_max_vp_index;
 EXPORT_SYMBOL_GPL(hv_max_vp_index);

@@ -73,12 +76,19 @@ static int hv_cpu_init(unsigned int cpu)
 	void **input_arg;
 	struct page *pg;

-	input_arg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg);
 	/* hv_cpu_init() can be called with IRQs disabled from hv_resume() */
-	pg = alloc_page(irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL);
+	pg = alloc_pages(irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL, hv_root_partition ?

1 : 0);
 	if (unlikely(!pg))
 		return -ENOMEM;
+
+	input_arg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg);
 	*input_arg = page_address(pg);
+	if (hv_root_partition) {
+		void **output_arg;
+
+		output_arg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
+		*output_arg = page_address(pg + 1);
+	}

 	hv_get_vp_index(msr_vp_index);

@@ -205,14 +215,23 @@ static int hv_cpu_die(unsigned int cpu)
 	unsigned int new_cpu;
 	unsigned long flags;
 	void **input_arg;
-	void *input_pg = NULL;
+	void *pg;

 	local_irq_save(flags);
 	input_arg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg);
-	input_pg = *input_arg;
+	pg = *input_arg;
 	*input_arg = NULL;
+
+	if (hv_root_partition) {
+		void **output_arg;
+
+		output_arg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
+		*output_arg = NULL;
+	}
+
 	local_irq_restore(flags);
-	free_page((unsigned long)input_pg);
+
+	free_pages((unsigned long)pg, hv_root_partition ? 1 : 0);

 	if (hv_vp_assist_page && hv_vp_assist_page[cpu])
 		wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, 0);

@@ -346,6 +365,12 @@ void __init hyperv_init(void)

 	BUG_ON(hyperv_pcpu_input_arg == NULL);

+	/* Allocate the per-CPU state for output arg for root */
+	if (hv_root_partition) {
+		hyperv_pcpu_output_arg = alloc_percpu(void *);
+		BUG_ON(hyperv_pcpu_output_arg == NULL);
+	}
+
 	/* Allocate percpu VP index */
 	hv_vp_index = kmalloc_array(num_possible_cpus(), sizeof(*hv_vp_index),
 				    GFP_KERNEL);

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index ac2b0d110f03..62d9390f1ddf 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h

@@ -76,6 +76,7 @@ static inline void hv_disable_stimer0_percpu_irq(int irq) {}
 #if IS_ENABLED(CONFIG_HYPERV)
 extern void *hv_hypercall_pg;
 extern void  __percpu  **hyperv_pcpu_input_arg;
+extern void  __percpu  **hyperv_pcpu_output_arg;

 static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
 {
--

2.20.1