Re: [RFC PATCH V3 13/16] x86/sev: Add Check of #HV event in path

From: Gupta, Pankaj
Date: Wed Mar 08 2023 - 11:18:46 EST


On 3/1/2023 12:11 PM, Gupta, Pankaj wrote:
On 1/22/2023 3:46 AM, Tianyu Lan wrote:
From: Tianyu Lan <tiala@xxxxxxxxxxxxx>

Add check_hv_pending() and check_hv_pending_after_irq() to
check queued #HV event when irq is disabled.

Signed-off-by: Tianyu Lan <tiala@xxxxxxxxxxxxx>
---
  arch/x86/entry/entry_64.S       | 18 +++++++++++++++
  arch/x86/include/asm/irqflags.h | 10 +++++++++
  arch/x86/kernel/sev.c           | 39 +++++++++++++++++++++++++++++++++
  3 files changed, 67 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 6baec7653f19..aec8dc4443d1 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1064,6 +1064,15 @@ SYM_CODE_END(paranoid_entry)
   * R15 - old SPEC_CTRL
   */
  SYM_CODE_START_LOCAL(paranoid_exit)
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+    /*
+     * If a #HV was delivered during execution and interrupts were
+     * disabled, then check if it can be handled before the iret
+     * (which may re-enable interrupts).
+     */
+    mov     %rsp, %rdi
+    call    check_hv_pending
+#endif
      UNWIND_HINT_REGS
      /*
@@ -1188,6 +1197,15 @@ SYM_CODE_START(error_entry)
  SYM_CODE_END(error_entry)
  SYM_CODE_START_LOCAL(error_return)
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+    /*
+     * If a #HV was delivered during execution and interrupts were
+     * disabled, then check if it can be handled before the iret
+     * (which may re-enable interrupts).
+     */
+    mov     %rsp, %rdi
+    call    check_hv_pending
+#endif
      UNWIND_HINT_REGS
      DEBUG_ENTRY_ASSERT_IRQS_OFF
      testb    $3, CS(%rsp)
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
index 7793e52d6237..fe46e59168dd 100644
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -14,6 +14,10 @@
  /*
   * Interrupt control:
   */
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+void check_hv_pending(struct pt_regs *regs);
+void check_hv_pending_irq_enable(void);
+#endif
  /* Declaration required for gcc < 4.9 to prevent -Werror=missing-prototypes */
  extern inline unsigned long native_save_fl(void);
@@ -43,12 +47,18 @@ static __always_inline void native_irq_disable(void)
  static __always_inline void native_irq_enable(void)
  {
      asm volatile("sti": : :"memory");
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+    check_hv_pending_irq_enable();
+#endif
  }
  static inline __cpuidle void native_safe_halt(void)
  {
      mds_idle_clear_cpu_buffers();
      asm volatile("sti; hlt": : :"memory");
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+    check_hv_pending_irq_enable();
+#endif
  }
  static inline __cpuidle void native_halt(void)
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a8862a2eff67..fe5e5e41433d 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -179,6 +179,45 @@ void noinstr __sev_es_ist_enter(struct pt_regs *regs)
      this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], new_ist);
  }
+static void do_exc_hv(struct pt_regs *regs)
+{
+    /* Handle #HV exception. */
+}
+
+void check_hv_pending(struct pt_regs *regs)
+{
+    if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+        return;
+
+    if ((regs->flags & X86_EFLAGS_IF) == 0)
+        return;

Will this return and prevent guest from executing NMI's
while irqs are disabled?

I think we need to handle NMI's even when irqs are disabled.

As we reset "no_further_signal" in hv_raw_handle_exception()
and return from check_hv_pending() when irqs are disabled, this
can result in loss/delay of NMI event?

Thanks,
Pankaj