On 16/07/15 22:29, Mario Smarduch wrote:
> This patch only saves and restores FP/SIMD registers on Guest access. To do
> this cptr_el2 FP/SIMD trap is set on Guest entry and later checked on exit.
> lmbench, hackbench show significant improvements, for 30-50% exits FP/SIMD
> context is not saved/restored
>
> Signed-off-by: Mario Smarduch <[email protected]>
So this patch seems to break 32bit guests on arm64. I've had a look,
squashed a few bugs that I dangerously overlooked during the review, but
it still doesn't work (it doesn't crash anymore, but I get random
illegal VFP instructions in 32bit guests).
I'd be glad if someone could eyeball the following patch and tell me
what's going wrong. If we don't find the root cause quickly enough, I'll
have to drop the series from -next, and that'd be a real shame.
Thanks,
M.
commit 5777dc55fbc170426a85e00c26002dd5a795cfa5
Author: Marc Zyngier <[email protected]>
Date: Wed Aug 5 16:53:01 2015 +0100
KVM: arm64: NOTAFIX: Prevent crash when 32bit guest uses VFP
Since we switch FPSIMD in a lazy way, access to FPEXC32_EL2
must be guarded by skip_fpsimd_state. Otherwise, all hell
break loose.
Also, FPEXC32_EL2 must be restored when we trap to EL2 to
enable floating point.
Note that while it prevents the host from catching fire, the
guest still doesn't work properly, and I don't understand why just
yet.
Not-really-signed-off-by: Marc Zyngier <[email protected]>
diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index c8e0c70..b53ec5d 100644
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -431,10 +431,12 @@
add x3, x2, #CPU_SYSREG_OFFSET(DACR32_EL2)
mrs x4, dacr32_el2
mrs x5, ifsr32_el2
- mrs x6, fpexc32_el2
stp x4, x5, [x3]
- str x6, [x3, #16]
+ skip_fpsimd_state x8, 3f
+ mrs x6, fpexc32_el2
+ str x6, [x3, #16]
+3:
skip_debug_state x8, 2f
mrs x7, dbgvcr32_el2
str x7, [x3, #24]
@@ -461,10 +463,8 @@
add x3, x2, #CPU_SYSREG_OFFSET(DACR32_EL2)
ldp x4, x5, [x3]
- ldr x6, [x3, #16]
msr dacr32_el2, x4
msr ifsr32_el2, x5
- msr fpexc32_el2, x6
skip_debug_state x8, 2f
ldr x7, [x3, #24]
@@ -669,12 +669,14 @@ __restore_debug:
ret
__save_fpsimd:
+ skip_fpsimd_state x3, 1f
save_fpsimd
- ret
+1: ret
__restore_fpsimd:
+ skip_fpsimd_state x3, 1f
restore_fpsimd
- ret
+1: ret
switch_to_guest_fpsimd:
push x4, lr
@@ -682,6 +684,7 @@ switch_to_guest_fpsimd:
mrs x2, cptr_el2
bic x2, x2, #CPTR_EL2_TFP
msr cptr_el2, x2
+ isb
mrs x0, tpidr_el2
@@ -692,6 +695,10 @@ switch_to_guest_fpsimd:
add x2, x0, #VCPU_CONTEXT
bl __restore_fpsimd
+ skip_32bit_state x3, 1f
+ ldr x4, [x2, #CPU_SYSREG_OFFSET(FPEXC32_EL2)]
+ msr fpexc32_el2, x4
+1:
pop x4, lr
pop x2, x3
pop x0, x1
@@ -754,9 +761,7 @@ __kvm_vcpu_return:
add x2, x0, #VCPU_CONTEXT
save_guest_regs
- skip_fpsimd_state x3, 1f
bl __save_fpsimd
-1:
bl __save_sysregs
skip_debug_state x3, 1f
@@ -777,9 +782,7 @@ __kvm_vcpu_return:
kern_hyp_va x2
bl __restore_sysregs
- skip_fpsimd_state x3, 1f
bl __restore_fpsimd
-1:
/* Clear FPSIMD and Trace trapping */
msr cptr_el2, xzr
--
Jazz is not dead. It just smells funny...
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