[kvm-unit-tests PATCH v2] x86: Set "APIC Software Enable" after APIC reset

[kvm-unit-tests PATCH v2] x86: Set "APIC Software Enable" after APIC reset

[Nadav Amit]

After the APIC is reset, some of its registers might be reset. As the
SDM says: "When IA32_APIC_BASE[11] is set to 0, prior initialization to
the APIC may be lost and the APIC may return to the state described in
Section 10.4.7.1". The SDM also says that after APIC reset "the
spurious-interrupt vector register is initialized to 000000FFH". This
means that after the APIC is reset it needs to be software-enabled
through the SPIV.

This is done one occasion, but there are other occasions that do not
software-enable the APIC after reset (e.g., __test_apic_id() and main()
in vmx.c). Reenable software-enable APIC in these cases.

Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Signed-off-by: Nadav Amit <nadav.amit@gmail.com>

---

v1->v2: Change 0xf0 to APIC_SPIV in one occasion [Krish]
---
 lib/x86/apic.c | 3 ++-
 x86/apic.c     | 1 -
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/x86/apic.c b/lib/x86/apic.c
index 2aeffbd..d4528bd 100644
--- a/lib/x86/apic.c
+++ b/lib/x86/apic.c
@@ -161,6 +161,7 @@ void reset_apic(void)
 {
     disable_apic();
     wrmsr(MSR_IA32_APICBASE, rdmsr(MSR_IA32_APICBASE) | APIC_EN);
+    apic_write(APIC_SPIV, 0x1ff);
 }
 
 u32 ioapic_read_reg(unsigned reg)
@@ -219,7 +220,7 @@ void set_irq_line(unsigned line, int val)
 void enable_apic(void)
 {
     printf("enabling apic\n");
-    xapic_write(0xf0, 0x1ff); /* spurious vector register */
+    xapic_write(APIC_SPIV, 0x1ff);
 }
 
 void mask_pic_interrupts(void)
diff --git a/x86/apic.c b/x86/apic.c
index 3eff588..7ef4a27 100644
--- a/x86/apic.c
+++ b/x86/apic.c
@@ -148,7 +148,6 @@ static void test_apic_disable(void)
     verify_disabled_apic_mmio();
 
     reset_apic();
-    apic_write(APIC_SPIV, 0x1ff);
     report("Local apic enabled in xAPIC mode",
 	   (rdmsr(MSR_IA32_APICBASE) & (APIC_EN | APIC_EXTD)) == APIC_EN);
     report("CPUID.1H:EDX.APIC[bit 9] is set", cpuid(1).d & (1 << 9));
-- 
2.17.1

Re: [kvm-unit-tests PATCH v2] x86: Set "APIC Software Enable" after APIC reset

[Paolo Bonzini]

On 18/05/19 17:48, Nadav Amit wrote:
> After the APIC is reset, some of its registers might be reset. As the
> SDM says: "When IA32_APIC_BASE[11] is set to 0, prior initialization to
> the APIC may be lost and the APIC may return to the state described in
> Section 10.4.7.1". The SDM also says that after APIC reset "the
> spurious-interrupt vector register is initialized to 000000FFH". This
> means that after the APIC is reset it needs to be software-enabled
> through the SPIV.
> 
> This is done one occasion, but there are other occasions that do not
> software-enable the APIC after reset (e.g., __test_apic_id() and main()
> in vmx.c). Reenable software-enable APIC in these cases.
> 
> Cc: Sean Christopherson <sean.j.christopherson@intel.com>
> Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
> 
> ---
> 
> v1->v2: Change 0xf0 to APIC_SPIV in one occasion [Krish]
> ---
>  lib/x86/apic.c | 3 ++-
>  x86/apic.c     | 1 -
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/x86/apic.c b/lib/x86/apic.c
> index 2aeffbd..d4528bd 100644
> --- a/lib/x86/apic.c
> +++ b/lib/x86/apic.c
> @@ -161,6 +161,7 @@ void reset_apic(void)
>  {
>      disable_apic();
>      wrmsr(MSR_IA32_APICBASE, rdmsr(MSR_IA32_APICBASE) | APIC_EN);
> +    apic_write(APIC_SPIV, 0x1ff);
>  }
>  
>  u32 ioapic_read_reg(unsigned reg)
> @@ -219,7 +220,7 @@ void set_irq_line(unsigned line, int val)
>  void enable_apic(void)
>  {
>      printf("enabling apic\n");
> -    xapic_write(0xf0, 0x1ff); /* spurious vector register */
> +    xapic_write(APIC_SPIV, 0x1ff);
>  }
>  
>  void mask_pic_interrupts(void)
> diff --git a/x86/apic.c b/x86/apic.c
> index 3eff588..7ef4a27 100644
> --- a/x86/apic.c
> +++ b/x86/apic.c
> @@ -148,7 +148,6 @@ static void test_apic_disable(void)
>      verify_disabled_apic_mmio();
>  
>      reset_apic();
> -    apic_write(APIC_SPIV, 0x1ff);
>      report("Local apic enabled in xAPIC mode",
>  	   (rdmsr(MSR_IA32_APICBASE) & (APIC_EN | APIC_EXTD)) == APIC_EN);
>      report("CPUID.1H:EDX.APIC[bit 9] is set", cpuid(1).d & (1 << 9));
> 

Queued, thanks.

Paolo