arm64: KVM: VHE: save and restore some PSTATE bits

PATCH gengdongjiu 1 participant 1 message Sep 6, 2017

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gengdongjiu

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2017-09-06 15:14 UTC #0 lore raw

Fix a typo.

It is similar with the PAN，when the guest traps to el2，it will reset the pstate.<http://pstate.PAN>UAO to 0, and continue run。In fact the host pstate.UAO<http://pstate.UAO> can be 1, but guest change it to 0 when trap to EL2, so after swich to host，need to check whether set pstate.UAO<http://pstate.UAO> again。

发件人：Vladimir Murzin 收件人：耿东久,marc.zyngier,[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],linux-kernel,[email protected],[email protected],Catalin Marinas 抄送：James Morse,张海斌,黄韶宇
时间：2017-09-06 22:41:09
主题:Re: [PATCH] arm64: KVM: VHE: save and restore some PSTATE bits

Quoted 8 lines · gengdongjiu

Hi, Vladimir
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Do you see effect of "PAN is unexpectedly enabled"?
In fact I did not encounter this case, but I think it can exist.
I think if host OS dynamically disable PAN, it wants the host kernel access the user space address space not through copy_to/from_user
API.
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Now if it is unexpectedly enabled, when host kernel still accesses the user space address, it will happen MMU fault exception.

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And this is expected! The only allowed channel for kernel <-> user is uaccess API.
I guess that you have test (and that great!) which violates that rule (for testing purpose, why not?) and now you are trying to fit kernel into it...
If you think that makes sense for it, we do not consider the paste.PAN in the world-switch. For the pstate.UAO issue, do you agree my fixing or you have other suggestion? Also to other reviewer. Thanks.

It would help if you give precise description on "pstate.UAO issue".

Thanks
Vladimir

Quoted 52 lines

arch/arm64/kvm/hyp/sysreg-sr.c +7 -1

index 9341376..c3dd761 100644
@@ -21,6 +21,8 @@
 #include <asm/kvm_asm.h>
 #include <asm/kvm_hyp.h>
 
+#include <asm/exec.h>
 
 /* Yes, this does nothing, on purpose */
 static void __hyp_text __sysreg_do_nothing(struct kvm_cpu_context *ctxt) { }

@@ -121,8 +123,13 @@ static void __hyp_text __sysreg_restore_state(struct kvm_cpu_context *ctxt)
        write_sysreg_el1(ctxt->gp_regs.spsr[KVM_SPSR_EL1],spsr);
 }
 
+static void __hyp_text __sysreg_restore_state_vhe(struct kvm_cpu_context *ctxt)
+{
+    uao_thread_switch(current);
+}
+
 static hyp_alternate_select(__sysreg_call_restore_host_state,
-                           __sysreg_restore_state, __sysreg_do_nothing,
+                           __sysreg_restore_state, __sysreg_restore_state_vhe,
                            ARM64_HAS_VIRT_HOST_EXTN);
 
 void __hyp_text __sysreg_restore_host_state(struct kvm_cpu_context *ctxt)

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Cheers
Vladimir
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Cheers
Vladimir
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Cheers
Vladimir
.

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