x86/realmode: Setup AP jump table

As part of the GHCB specification, the booting of APs under SEV-ES
requires an AP jump table when transitioning from one layer of code to
another (e.g. when going from UEFI to the OS). As a result, each layer
that parks an AP must provide the physical address of an AP jump table
to the next layer via the hypervisor.

Upon booting of the kernel, read the AP jump table address from the
hypervisor. Under SEV-ES, APs are started using the INIT-SIPI-SIPI
sequence. Before issuing the first SIPI request for an AP, the start
CS and IP is programmed into the AP jump table. Upon issuing the SIPI
request, the AP will awaken and jump to that start CS:IP address.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
[ jroedel@suse.de: - Adapted to different code base
                   - Moved AP table setup from SIPI sending path to
		     real-mode setup code
		   - Fix sparse warnings ]
Co-developed-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-67-joro@8bytes.org

1 files changed, 69 insertions, 0 deletions

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 6d89df9f29dc..9ad36ce92b82 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -21,6 +21,7 @@
 #include <linux/mm.h>
 
 #include <asm/cpu_entry_area.h>
+#include <asm/stacktrace.h>
 #include <asm/sev-es.h>
 #include <asm/insn-eval.h>
 #include <asm/fpu/internal.h>
@@ -214,6 +215,9 @@ static __always_inline void sev_es_put_ghcb(struct ghcb_state *state)
 	}
 }
 
+/* Needed in vc_early_forward_exception */
+void do_early_exception(struct pt_regs *regs, int trapnr);
+
 static inline u64 sev_es_rd_ghcb_msr(void)
 {
 	return __rdmsr(MSR_AMD64_SEV_ES_GHCB);
@@ -402,6 +406,71 @@ static bool vc_slow_virt_to_phys(struct ghcb *ghcb, struct es_em_ctxt *ctxt,
 /* Include code shared with pre-decompression boot stage */
 #include "sev-es-shared.c"
 
+static u64 get_jump_table_addr(void)
+{
+	struct ghcb_state state;
+	unsigned long flags;
+	struct ghcb *ghcb;
+	u64 ret = 0;
+
+	local_irq_save(flags);
+
+	ghcb = sev_es_get_ghcb(&state);
+
+	vc_ghcb_invalidate(ghcb);
+	ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_AP_JUMP_TABLE);
+	ghcb_set_sw_exit_info_1(ghcb, SVM_VMGEXIT_GET_AP_JUMP_TABLE);
+	ghcb_set_sw_exit_info_2(ghcb, 0);
+
+	sev_es_wr_ghcb_msr(__pa(ghcb));
+	VMGEXIT();
+
+	if (ghcb_sw_exit_info_1_is_valid(ghcb) &&
+	    ghcb_sw_exit_info_2_is_valid(ghcb))
+		ret = ghcb->save.sw_exit_info_2;
+
+	sev_es_put_ghcb(&state);
+
+	local_irq_restore(flags);
+
+	return ret;
+}
+
+int sev_es_setup_ap_jump_table(struct real_mode_header *rmh)
+{
+	u16 startup_cs, startup_ip;
+	phys_addr_t jump_table_pa;
+	u64 jump_table_addr;
+	u16 __iomem *jump_table;
+
+	jump_table_addr = get_jump_table_addr();
+
+	/* On UP guests there is no jump table so this is not a failure */
+	if (!jump_table_addr)
+		return 0;
+
+	/* Check if AP Jump Table is page-aligned */
+	if (jump_table_addr & ~PAGE_MASK)
+		return -EINVAL;
+
+	jump_table_pa = jump_table_addr & PAGE_MASK;
+
+	startup_cs = (u16)(rmh->trampoline_start >> 4);
+	startup_ip = (u16)(rmh->sev_es_trampoline_start -
+			   rmh->trampoline_start);
+
+	jump_table = ioremap_encrypted(jump_table_pa, PAGE_SIZE);
+	if (!jump_table)
+		return -EIO;
+
+	writew(startup_ip, &jump_table[0]);
+	writew(startup_cs, &jump_table[1]);
+
+	iounmap(jump_table);
+
+	return 0;
+}
+
 static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
 {
 	struct pt_regs *regs = ctxt->regs;