[PATCH v4 2/6] x86/sev-es: Disable IRQs while GHCB is active

Joerg Roedel
Thu, 10 Jun 2021 09:11:37 -0000

The #VC handler only cares about IRQs being disabled while the GHCB is
active, as it must not be interrupted by something which could cause
another #VC while it holds the GHCB (NMI is the exception for which the
backup GHCB is there).

Make sure nothing interrupts the code path while the GHCB is active by
disabling IRQs in sev_es_get_ghcb() and restoring the previous irq state
in sev_es_put_ghcb().

Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 arch/x86/kernel/sev.c | 39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 4fd997bbf059..2a922d1b03c8 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -192,14 +192,23 @@ void noinstr __sev_es_ist_exit(void)
 	this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], *(unsigned long *)ist);
 }

-static __always_inline struct ghcb *sev_es_get_ghcb(struct ghcb_state *state)
+static __always_inline struct ghcb *sev_es_get_ghcb(struct ghcb_state *state,
+						    unsigned long *flags)
 {
 	struct sev_es_runtime_data *data;
 	struct ghcb *ghcb;

+	/*
+	 * Nothing shall interrupt this code path while holding the per-cpu
+	 * GHCB. The backup GHCB is only for NMIs interrupting this path.
+	 */
+	local_irq_save(*flags);
+
 	data = this_cpu_read(runtime_data);
 	ghcb = &data->ghcb_page;

+
+
 	if (unlikely(data->ghcb_active)) {
 		/* GHCB is already in use - save its contents */

@@ -479,7 +488,8 @@ static enum es_result vc_slow_virt_to_phys(struct ghcb
*ghcb, struct es_em_ctxt
 /* Include code shared with pre-decompression boot stage */
 #include "sev-shared.c"

-static __always_inline void sev_es_put_ghcb(struct ghcb_state *state)
+static __always_inline void sev_es_put_ghcb(struct ghcb_state *state,
+					    unsigned long flags)
 {
 	struct sev_es_runtime_data *data;
 	struct ghcb *ghcb;
@@ -500,14 +510,17 @@ static __always_inline void sev_es_put_ghcb(struct
ghcb_state *state)
 		vc_ghcb_invalidate(ghcb);
 		data->ghcb_active = false;
 	}
+
+	local_irq_restore(flags);
 }

 void noinstr __sev_es_nmi_complete(void)
 {
 	struct ghcb_state state;
+	unsigned long flags;
 	struct ghcb *ghcb;

-	ghcb = sev_es_get_ghcb(&state);
+	ghcb = sev_es_get_ghcb(&state, &flags);

 	vc_ghcb_invalidate(ghcb);
 	ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_NMI_COMPLETE);
@@ -517,7 +530,7 @@ void noinstr __sev_es_nmi_complete(void)
 	sev_es_wr_ghcb_msr(__pa_nodebug(ghcb));
 	VMGEXIT();

-	sev_es_put_ghcb(&state);
+	sev_es_put_ghcb(&state, flags);
 }

 static u64 get_jump_table_addr(void)
@@ -527,9 +540,7 @@ static u64 get_jump_table_addr(void)
 	struct ghcb *ghcb;
 	u64 ret = 0;

-	local_irq_save(flags);
-
-	ghcb = sev_es_get_ghcb(&state);
+	ghcb = sev_es_get_ghcb(&state, &flags);

 	vc_ghcb_invalidate(ghcb);
 	ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_AP_JUMP_TABLE);
@@ -543,9 +554,7 @@ static u64 get_jump_table_addr(void)
 	    ghcb_sw_exit_info_2_is_valid(ghcb))
 		ret = ghcb->save.sw_exit_info_2;

-	sev_es_put_ghcb(&state);
-
-	local_irq_restore(flags);
+	sev_es_put_ghcb(&state, flags);

 	return ret;
 }
@@ -666,9 +675,10 @@ static bool __init sev_es_setup_ghcb(void)
 static void sev_es_ap_hlt_loop(void)
 {
 	struct ghcb_state state;
+	unsigned long flags;
 	struct ghcb *ghcb;

-	ghcb = sev_es_get_ghcb(&state);
+	ghcb = sev_es_get_ghcb(&state, &flags);

 	while (true) {
 		vc_ghcb_invalidate(ghcb);
@@ -685,7 +695,7 @@ static void sev_es_ap_hlt_loop(void)
 			break;
 	}

-	sev_es_put_ghcb(&state);
+	sev_es_put_ghcb(&state, flags);
 }

 /*
@@ -1333,6 +1343,7 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 	struct ghcb_state state;
 	struct es_em_ctxt ctxt;
 	enum es_result result;
+	unsigned long flags;
 	struct ghcb *ghcb;

 	/*
@@ -1353,7 +1364,7 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 	 * keep the IRQs disabled to protect us against concurrent TLB flushes.
 	 */

-	ghcb = sev_es_get_ghcb(&state);
+	ghcb = sev_es_get_ghcb(&state, &flags);

 	vc_ghcb_invalidate(ghcb);
 	result = vc_init_em_ctxt(&ctxt, regs, error_code);
@@ -1361,7 +1372,7 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 	if (result == ES_OK)
 		result = vc_handle_exitcode(&ctxt, ghcb, error_code);

-	sev_es_put_ghcb(&state);
+	sev_es_put_ghcb(&state, flags);

 	/* Done - now check the result */
 	switch (result) {
--
2.31.1