[RFC PATCH v2 2/2] KVM: x86: Allow Qemu/KVM to use PVH entry point

[Maran Wilson]

For certain applications it is desirable to rapidly boot a KVM virtual
machine. In cases where legacy hardware and software support within the
guest is not needed, Qemu should be able to boot directly into the
uncompressed Linux kernel binary without the need to run firmware.

There already exists an ABI to allow this for Xen PVH guests and the ABI
is supported by Linux and FreeBSD:

   https://xenbits.xen.org/docs/unstable/misc/pvh.html

This patch enables Qemu to use that same entry point for booting KVM
guests.
---
 arch/x86/xen/enlighten_pvh.c | 48 ++++++++++++++++++++++++++++++--------------
 1 file changed, 33 insertions(+), 15 deletions(-)

diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
index 98ab176..f11fbfc 100644
--- a/arch/x86/xen/enlighten_pvh.c
+++ b/arch/x86/xen/enlighten_pvh.c
@@ -31,21 +31,35 @@ static void xen_pvh_arch_setup(void)
 		acpi_irq_model = ACPI_IRQ_MODEL_PLATFORM;
 }
 
-static void __init init_pvh_bootparams(void)
+static void __init init_pvh_bootparams(bool xen_guest)
 {
 	struct xen_memory_map memmap;
 	int rc;
 
 	memset(&pvh_bootparams, 0, sizeof(pvh_bootparams));
 
-	memmap.nr_entries = ARRAY_SIZE(pvh_bootparams.e820_table);
-	set_xen_guest_handle(memmap.buffer, pvh_bootparams.e820_table);
-	rc = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap);
-	if (rc) {
-		xen_raw_printk("XENMEM_memory_map failed (%d)\n", rc);
+	if ((pvh_start_info.version > 0) && (pvh_start_info.memmap_entries)) {
+		struct boot_e820_entry *ep;
+		int idx;
+
+		ep = __va(pvh_start_info.memmap_paddr);
+		pvh_bootparams.e820_entries = pvh_start_info.memmap_entries;
+
+		for (idx = 0; idx < pvh_bootparams.e820_entries ; idx++, ep++)
+			pvh_bootparams.e820_table[idx] = *ep;
+	} else if (xen_guest) {
+		memmap.nr_entries = ARRAY_SIZE(pvh_bootparams.e820_table);
+		set_xen_guest_handle(memmap.buffer, pvh_bootparams.e820_table);
+		rc = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap);
+		if (rc) {
+			xen_raw_printk("XENMEM_memory_map failed (%d)\n", rc);
+			BUG();
+		}
+		pvh_bootparams.e820_entries = memmap.nr_entries;
+	} else {
+		xen_raw_printk("Error: Could not find memory map\n");
 		BUG();
 	}
-	pvh_bootparams.e820_entries = memmap.nr_entries;
 
 	if (pvh_bootparams.e820_entries < E820_MAX_ENTRIES_ZEROPAGE - 1) {
 		pvh_bootparams.e820_table[pvh_bootparams.e820_entries].addr =
@@ -76,7 +90,7 @@ static void __init init_pvh_bootparams(void)
 	 * environment (i.e. hardware_subarch 0).
 	 */
 	pvh_bootparams.hdr.version = 0x212;
-	pvh_bootparams.hdr.type_of_loader = (9 << 4) | 0; /* Xen loader */
+	pvh_bootparams.hdr.type_of_loader = ((xen_guest ? 0x9 : 0xb) << 4) | 0;
 }
 
 /*
@@ -85,8 +99,10 @@ static void __init init_pvh_bootparams(void)
  */
 void __init xen_prepare_pvh(void)
 {
-	u32 msr;
+
+	u32 msr = xen_cpuid_base();
 	u64 pfn;
+	bool xen_guest = !!msr;
 
 	if (pvh_start_info.magic != XEN_HVM_START_MAGIC_VALUE) {
 		xen_raw_printk("Error: Unexpected magic value (0x%08x)\n",
@@ -94,13 +110,15 @@ void __init xen_prepare_pvh(void)
 		BUG();
 	}
 
-	xen_pvh = 1;
+	if (xen_guest) {
+		xen_pvh = 1;
 
-	msr = cpuid_ebx(xen_cpuid_base() + 2);
-	pfn = __pa(hypercall_page);
-	wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32));
+		msr = cpuid_ebx(msr + 2);
+		pfn = __pa(hypercall_page);
+		wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32));
 
-	init_pvh_bootparams();
+		x86_init.oem.arch_setup = xen_pvh_arch_setup;
+	}
 
-	x86_init.oem.arch_setup = xen_pvh_arch_setup;
+	init_pvh_bootparams(xen_guest);
 }
-- 
1.8.3.1