[PATCH v2 08/17] x86/hyperv: handling hypercall page setup for root

[Wei Liu]

When Linux is running as the root partition, the hypercall page will
have already been setup by Hyper-V. Copy the content over to the
allocated page.

The suspend, resume and cleanup paths remain untouched because they are
not supported in this setup yet.

Signed-off-by: Lillian Grassin-Drake <ligrassi@xxxxxxxxxxxxx>
Signed-off-by: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>
Signed-off-by: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx>
Co-Developed-by: Lillian Grassin-Drake <ligrassi@xxxxxxxxxxxxx>
Co-Developed-by: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>
Co-Developed-by: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
---
 arch/x86/hyperv/hv_init.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 73b0fb851f76..9fcaf741be99 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -25,6 +25,7 @@
 #include <linux/cpuhotplug.h>
 #include <linux/syscore_ops.h>
 #include <clocksource/hyperv_timer.h>
+#include <linux/highmem.h>
 
 /* Is Linux running as the root partition? */
 bool hv_root_partition;
@@ -438,8 +439,35 @@ void __init hyperv_init(void)
 
 	rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 	hypercall_msr.enable = 1;
-	hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
-	wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
+
+	if (hv_root_partition) {
+		struct page *pg;
+		void *src, *dst;
+
+		/*
+		 * For the root partition, the hypervisor will set up its
+		 * hypercall page. The hypervisor guarantees it will not show
+		 * up in the root's address space. The root can't change the
+		 * location of the hypercall page.
+		 *
+		 * Order is important here. We must enable the hypercall page
+		 * so it is populated with code, then copy the code to an
+		 * executable page.
+		 */
+		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
+
+		pg = vmalloc_to_page(hv_hypercall_pg);
+		dst = kmap(pg);
+		src = memremap(hypercall_msr.guest_physical_address << PAGE_SHIFT, PAGE_SIZE,
+				MEMREMAP_WB);
+		BUG_ON(!(src && dst));
+		memcpy(dst, src, PAGE_SIZE);
+		memunmap(src);
+		kunmap(pg);
+	} else {
+		hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
+		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
+	}
 
 	/*
 	 * Ignore any errors in setting up stimer clockevents
-- 
2.20.1