On 17.07.14 18:27, Alexander Graf wrote:
On 17.07.14 18:24, Bharat.Bhushan@xxxxxxxxxxxxx wrote:
-----Original Message-----
From: Alexander Graf [mailto:agraf@xxxxxxx]
Sent: Thursday, July 17, 2014 9:41 PM
To: Bhushan Bharat-R65777; kvm-ppc@xxxxxxxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx; Wood Scott-B07421; Yoder Stuart-B08248
Subject: Re: [PATCH] kvm: ppc: booke: Restore SPRG3 when entering guest
On 16.07.14 08:02, Bharat Bhushan wrote:
SPRG3 is guest accessible and SPRG3 can be clobbered by host or
another guest, So this need to be restored when loading guest state.
Signed-off-by: Bharat Bhushan <Bharat.Bhushan@xxxxxxxxxxxxx>
---
arch/powerpc/kvm/booke_interrupts.S | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/powerpc/kvm/booke_interrupts.S
b/arch/powerpc/kvm/booke_interrupts.S
index 2c6deb5ef..0d3403f 100644
--- a/arch/powerpc/kvm/booke_interrupts.S
+++ b/arch/powerpc/kvm/booke_interrupts.S
@@ -459,6 +459,8 @@ lightweight_exit:
* written directly to the shared area, so we
* need to reload them here with the guest's values.
*/
+ PPC_LD(r3, VCPU_SHARED_SPRG3, r5)
+ mtspr SPRN_SPRG3, r3
We also need to restore it when resuming the host, no?
I do not think host expect some meaningful value when returning from
guest, same true for SPRG4-7.
So there seems no reason to save host values and restore them.
Hmm - arch/powerpc/include/asm/reg.h says:
* All 32-bit:
* - SPRG3 current thread_info pointer
* (virtual on BookE, physical on others)
but I can indeed find no trace of usage anywhere. This at least needs
to go into the patch description.
Bah - it obviously is used. It's SPRN_SPRG_THREAD. And it's so
incredibly important that I have no idea how we could possibly run
without switching the host value back in very early. And even then our
interrupt handlers wouldn't work anymore.
This is more complicated :).
Alex
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
