powerpc/pseries/svm: Unshare all pages before kexecing a new kernel

A new kernel deserves a clean slate. Any pages shared with the hypervisor
is unshared before invoking the new kernel. However there are exceptions.
If the new kernel is invoked to dump the current kernel, or if there is a
explicit request to preserve the state of the current kernel, unsharing
of pages is skipped.

NOTE: While testing crashkernel, make sure at least 256M is reserved for
crashkernel. Otherwise SWIOTLB allocation will fail and crash kernel will
fail to boot.
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190820021326.6884-11-bauerman@linux.ibm.com

arch/powerpc/include/asm/ultravisor-api.h

@@ -28,5 +28,6 @@
 #define UV_ESM				0xF110
 #define UV_SHARE_PAGE			0xF130
 #define UV_UNSHARE_PAGE			0xF134
+#define UV_UNSHARE_ALL_PAGES		0xF140
 
 #endif /* _ASM_POWERPC_ULTRAVISOR_API_H */

arch/powerpc/include/asm/ultravisor.h

@@ -41,4 +41,9 @@ static inline int uv_unshare_page(u64 pfn, u64 npages)
 	return ucall_norets(UV_UNSHARE_PAGE, pfn, npages);
 }
 
+static inline int uv_unshare_all_pages(void)
+{
+	return ucall_norets(UV_UNSHARE_ALL_PAGES);
+}
+
 #endif	/* _ASM_POWERPC_ULTRAVISOR_H */

arch/powerpc/kernel/machine_kexec_64.c

@@ -29,6 +29,8 @@
 #include <asm/smp.h>
 #include <asm/hw_breakpoint.h>
 #include <asm/asm-prototypes.h>
+#include <asm/svm.h>
+#include <asm/ultravisor.h>
 
 int default_machine_kexec_prepare(struct kimage *image)
 {
@@ -327,6 +329,13 @@ void default_machine_kexec(struct kimage *image)
 #ifdef CONFIG_PPC_PSERIES
 	kexec_paca.lppaca_ptr = NULL;
 #endif
+
+	if (is_secure_guest() && !(image->preserve_context ||
+				   image->type == KEXEC_TYPE_CRASH)) {
+		uv_unshare_all_pages();
+		printk("kexec: Unshared all shared pages.\n");
+	}
+
 	paca_ptrs[kexec_paca.paca_index] = &kexec_paca;
 
 	setup_paca(&kexec_paca);