From: James Morse <james.morse@arm.com> To: kvmarm@lists.cs.columbia.edu Cc: Marc Zyngier <marc.zyngier@arm.com>, linux-arm-kernel@lists.infradead.org Subject: [PATCH] KVM: arm64: stop propagating DAIF flags between kernel and VHE's world switch Date: Thu, 10 Aug 2017 12:30:21 +0100 [thread overview] Message-ID: <20170810113021.1110-1-james.morse@arm.com> (raw) KVM calls __kvm_vcpu_run() in a loop with interrupts masked for the duration of the call. On a non-vhe system we HVC to EL2 and the host DAIF flags are save/restored via the SPSR. On a system with vhe, we branch to the EL2 code because the kernel also runs at EL2. This means the other kernel DAIF flags propagate into KVMs EL2 code. The same happens in reverse, we take an exception to exit the guest and all the flags are masked. __guest_exit() unmasks SError, and we return with these flags through world switch and back into the host kernel. KVM unmasks interrupts as part of its __kvm_vcpu_run(), but debug exceptions remain disabled due to the guest exit exception, (as does SError: today this is the only time SError is unmasked in the kernel). The flags stay in this state until we return to userspace. We have a __vhe_hyp_call() function that does the isb that we implicitly have on non-vhe systems, add the DAIF save/restore here, instead of in __sysreg_{save,restore}_host_state() which would require an extra isb() between the hosts VBAR_EL1 being restored and DAIF being restored. Signed-off-by: James Morse <james.morse@arm.com> --- I don't like the host DAIF context being stored on the stack instead of kvm_host_cpu_state, but this should only be a problem for returns that don't go through __vhe_hyp_call(). That should just be hyp_panic() where we want to change DAIF anyway. If you want a fixes tag for this, I think its: Fixes: b81125c791a2 ("arm64: KVM: VHE: Patch out use of HVC") While this won't conflict with v3 of the RAS+IESB series, it will depend on this patches behaviour: Without this patch you will have SError unmasked on host->guest world switch, a v8.2 RAS error arriving during this window will HYP panic, but this is already the case today for guest->host. arch/arm64/kvm/hyp/hyp-entry.S | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S index 5170ce1021da..5eaa336e5dd9 100644 --- a/arch/arm64/kvm/hyp/hyp-entry.S +++ b/arch/arm64/kvm/hyp/hyp-entry.S @@ -42,6 +42,11 @@ .endm ENTRY(__vhe_hyp_call) + /* HVC->ERET implicitly save/restore DAIF, we do it manually here. */ + mrs x9, daif + str x9, [sp, #-16]! + msr daifset, #0xf + do_el2_call /* * We used to rely on having an exception return to get @@ -50,6 +55,14 @@ ENTRY(__vhe_hyp_call) * before returning to the rest of the kernel. */ isb + + /* + * World-switch changes VBAR_EL1, we can only restore DAIF after + * the hosts value has been synchronised by the above isb. + */ + ldr x9, [sp], #16 + msr daif, x9 + ret ENDPROC(__vhe_hyp_call) -- 2.13.3
WARNING: multiple messages have this Message-ID (diff)
From: james.morse@arm.com (James Morse) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH] KVM: arm64: stop propagating DAIF flags between kernel and VHE's world switch Date: Thu, 10 Aug 2017 12:30:21 +0100 [thread overview] Message-ID: <20170810113021.1110-1-james.morse@arm.com> (raw) KVM calls __kvm_vcpu_run() in a loop with interrupts masked for the duration of the call. On a non-vhe system we HVC to EL2 and the host DAIF flags are save/restored via the SPSR. On a system with vhe, we branch to the EL2 code because the kernel also runs at EL2. This means the other kernel DAIF flags propagate into KVMs EL2 code. The same happens in reverse, we take an exception to exit the guest and all the flags are masked. __guest_exit() unmasks SError, and we return with these flags through world switch and back into the host kernel. KVM unmasks interrupts as part of its __kvm_vcpu_run(), but debug exceptions remain disabled due to the guest exit exception, (as does SError: today this is the only time SError is unmasked in the kernel). The flags stay in this state until we return to userspace. We have a __vhe_hyp_call() function that does the isb that we implicitly have on non-vhe systems, add the DAIF save/restore here, instead of in __sysreg_{save,restore}_host_state() which would require an extra isb() between the hosts VBAR_EL1 being restored and DAIF being restored. Signed-off-by: James Morse <james.morse@arm.com> --- I don't like the host DAIF context being stored on the stack instead of kvm_host_cpu_state, but this should only be a problem for returns that don't go through __vhe_hyp_call(). That should just be hyp_panic() where we want to change DAIF anyway. If you want a fixes tag for this, I think its: Fixes: b81125c791a2 ("arm64: KVM: VHE: Patch out use of HVC") While this won't conflict with v3 of the RAS+IESB series, it will depend on this patches behaviour: Without this patch you will have SError unmasked on host->guest world switch, a v8.2 RAS error arriving during this window will HYP panic, but this is already the case today for guest->host. arch/arm64/kvm/hyp/hyp-entry.S | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S index 5170ce1021da..5eaa336e5dd9 100644 --- a/arch/arm64/kvm/hyp/hyp-entry.S +++ b/arch/arm64/kvm/hyp/hyp-entry.S @@ -42,6 +42,11 @@ .endm ENTRY(__vhe_hyp_call) + /* HVC->ERET implicitly save/restore DAIF, we do it manually here. */ + mrs x9, daif + str x9, [sp, #-16]! + msr daifset, #0xf + do_el2_call /* * We used to rely on having an exception return to get @@ -50,6 +55,14 @@ ENTRY(__vhe_hyp_call) * before returning to the rest of the kernel. */ isb + + /* + * World-switch changes VBAR_EL1, we can only restore DAIF after + * the hosts value has been synchronised by the above isb. + */ + ldr x9, [sp], #16 + msr daif, x9 + ret ENDPROC(__vhe_hyp_call) -- 2.13.3
next reply other threads:[~2017-08-10 11:30 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-08-10 11:30 James Morse [this message] 2017-08-10 11:30 ` [PATCH] KVM: arm64: stop propagating DAIF flags between kernel and VHE's world switch James Morse 2017-08-24 15:23 ` Christoffer Dall 2017-08-24 15:23 ` Christoffer Dall 2017-08-29 17:10 ` James Morse 2017-08-29 17:10 ` James Morse 2017-08-30 8:33 ` Christoffer Dall 2017-08-30 8:33 ` Christoffer Dall 2017-08-30 18:01 ` James Morse 2017-08-30 18:01 ` James Morse 2017-08-30 19:04 ` Christoffer Dall 2017-08-30 19:04 ` Christoffer Dall
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20170810113021.1110-1-james.morse@arm.com \ --to=james.morse@arm.com \ --cc=kvmarm@lists.cs.columbia.edu \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=marc.zyngier@arm.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.