x86/mm, kexec: Allow kexec to be used with SME

Provide support so that kexec can be used to boot a kernel when SME is
enabled.

Support is needed to allocate pages for kexec without encryption.  This
is needed in order to be able to reboot in the kernel in the same manner
as originally booted.

Additionally, when shutting down all of the CPUs we need to be sure to
flush the caches and then halt. This is needed when booting from a state
where SME was not active into a state where SME is active (or vice-versa).
Without these steps, it is possible for cache lines to exist for the same
physical location but tagged both with and without the encryption bit. This
can cause random memory corruption when caches are flushed depending on
which cacheline is written last.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: <kexec@lists.infradead.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Toshimitsu Kani <toshi.kani@hpe.com>
Cc: kasan-dev@googlegroups.com
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-efi@vger.kernel.org
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/b95ff075db3e7cd545313f2fb609a49619a09625.1500319216.git.thomas.lendacky@amd.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 21 insertions, 1 deletions

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index cb0a30473c23..9cf8daacc046 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -87,7 +87,7 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
 		set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
 	}
 	pte = pte_offset_kernel(pmd, vaddr);
-	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC));
+	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC_NOENC));
 	return 0;
 err:
 	free_transition_pgtable(image);
@@ -115,6 +115,7 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
 		.alloc_pgt_page	= alloc_pgt_page,
 		.context	= image,
 		.page_flag	= __PAGE_KERNEL_LARGE_EXEC,
+		.kernpg_flag	= _KERNPG_TABLE_NOENC,
 	};
 	unsigned long mstart, mend;
 	pgd_t *level4p;
@@ -602,3 +603,22 @@ void arch_kexec_unprotect_crashkres(void)
 {
 	kexec_mark_crashkres(false);
 }
+
+int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, gfp_t gfp)
+{
+	/*
+	 * If SME is active we need to be sure that kexec pages are
+	 * not encrypted because when we boot to the new kernel the
+	 * pages won't be accessed encrypted (initially).
+	 */
+	return set_memory_decrypted((unsigned long)vaddr, pages);
+}
+
+void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages)
+{
+	/*
+	 * If SME is active we need to reset the pages back to being
+	 * an encrypted mapping before freeing them.
+	 */
+	set_memory_encrypted((unsigned long)vaddr, pages);
+}