From: Vitaly Kuznetsov <vkuznets@redhat.com> Sent: Tuesday, March 2, 2021 4:57 AM

Michael Kelley [off-list ref] writes:

quoted

The Hyper-V page allocator functions are implemented in an architecture
neutral way.  Move them into the architecture neutral VMbus module so
a separate implementation for ARM64 is not needed.

No functional change.

Signed-off-by: Michael Kelley <redacted>
Reviewed-by: Boqun Feng <redacted>
---
 arch/x86/hyperv/hv_init.c       | 22 ----------------------
 arch/x86/include/asm/mshyperv.h |  5 -----
 drivers/hv/hv.c                 | 36 ++++++++++++++++++++++++++++++++++++
 include/asm-generic/mshyperv.h  |  4 ++++
 4 files changed, 40 insertions(+), 27 deletions(-)

[snip]

quoted

 /*
+ * Functions for allocating and freeing memory with size and
+ * alignment HV_HYP_PAGE_SIZE. These functions are needed because
+ * the guest page size may not be the same as the Hyper-V page
+ * size. We depend upon kmalloc() aligning power-of-two size
+ * allocations to the allocation size boundary, so that the
+ * allocated memory appears to Hyper-V as a page of the size
+ * it expects.
+ */
+
+void *hv_alloc_hyperv_page(void)
+{
+	BUILD_BUG_ON(PAGE_SIZE <  HV_HYP_PAGE_SIZE);
+
+	if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
+		return (void *)__get_free_page(GFP_KERNEL);
+	else
+		return kmalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);

PAGE_SIZE and HV_HYP_PAGE_SIZE are known compile-time and in case this
won't change in the future we can probably write this as

#if PAGE_SIZE == HV_HYP_PAGE_SIZE
       return (void *)__get_free_page(GFP_KERNEL);
#else
       return kmalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
#endif

(not sure if the output is going to be any different with e.g. gcc's '-O2')

I looked at the generated code, and the compiler does the right
thing on both x86/x64 and on ARM64.  I'd rather leave the code
as is so that both legs of the 'if' statement get checked by the
compiler regardless of whether PAGE_SIZE == HV_HYP_PAGE_SIZE.

Michael

quoted

+}
+
+void *hv_alloc_hyperv_zeroed_page(void)
+{
+	if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
+		return (void *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
+	else
+		return kzalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
+}
+
+void hv_free_hyperv_page(unsigned long addr)
+{
+	if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
+		free_page(addr);
+	else
+		kfree((void *)addr);
+}
+
+/*