[PATCH v4 2/5] x86: hv: Add functions to allocate/deallocate page for Hyper-V

[Maya Nakamura]

Introduce two new functions, hv_alloc_hyperv_page() and
hv_free_hyperv_page(), to allocate/deallocate memory with the size and
alignment that Hyper-V expects as a page. Although currently they are
not used, they are ready to be used to allocate/deallocate memory on x86
when their ARM64 counterparts are implemented, keeping symmetry between
architectures with potentially different guest page sizes.

Link: https://lore.kernel.org/lkml/alpine.DEB.2.21.1906272334560.32342@xxxxxxxxxxxxxxxxxxxxxxx/
Link: https://lore.kernel.org/lkml/87muindr9c.fsf@xxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Maya Nakamura <m.maya.nakamura@xxxxxxxxx>
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 arch/x86/hyperv/hv_init.c       | 14 ++++++++++++++
 arch/x86/include/asm/mshyperv.h |  5 ++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 0e033ef11a9f..e8960a83add7 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -37,6 +37,20 @@ EXPORT_SYMBOL_GPL(hyperv_pcpu_input_arg);
 u32 hv_max_vp_index;
 EXPORT_SYMBOL_GPL(hv_max_vp_index);
 
+void *hv_alloc_hyperv_page(void)
+{
+	BUILD_BUG_ON(PAGE_SIZE != HV_HYP_PAGE_SIZE);
+
+	return (void *)__get_free_page(GFP_KERNEL);
+}
+EXPORT_SYMBOL_GPL(hv_alloc_hyperv_page);
+
+void hv_free_hyperv_page(unsigned long addr)
+{
+	free_page(addr);
+}
+EXPORT_SYMBOL_GPL(hv_free_hyperv_page);
+
 static int hv_cpu_init(unsigned int cpu)
 {
 	u64 msr_vp_index;
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 2a793bf6ebb0..32ec9df39a99 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -218,7 +218,8 @@ static inline struct hv_vp_assist_page *hv_get_vp_assist_page(unsigned int cpu)
 
 void __init hyperv_init(void);
 void hyperv_setup_mmu_ops(void);
-
+void *hv_alloc_hyperv_page(void);
+void hv_free_hyperv_page(unsigned long addr);
 void hyperv_reenlightenment_intr(struct pt_regs *regs);
 void set_hv_tscchange_cb(void (*cb)(void));
 void clear_hv_tscchange_cb(void);
@@ -241,6 +242,8 @@ static inline void hv_apic_init(void) {}
 #else /* CONFIG_HYPERV */
 static inline void hyperv_init(void) {}
 static inline void hyperv_setup_mmu_ops(void) {}
+static inline void *hv_alloc_hyperv_page(void) { return NULL; }
+static inline void hv_free_hyperv_page(unsigned long addr) {}
 static inline void set_hv_tscchange_cb(void (*cb)(void)) {}
 static inline void clear_hv_tscchange_cb(void) {}
 static inline void hyperv_stop_tsc_emulation(void) {};
-- 
2.17.1