From: Stephen Boyd <swboyd@chromium.org>
To: Will Deacon <will@kernel.org>, Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Andre Przywara <andre.przywara@arm.com>,
Steven Price <steven.price@arm.com>,
Marc Zyngier <maz@kernel.org>,
stable@vger.kernel.org
Subject: [PATCH v3] KVM: arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesn't return SMCCC_RET_NOT_REQUIRED
Date: Fri, 23 Oct 2020 08:47:50 -0700 [thread overview]
Message-ID: <20201023154751.1973872-1-swboyd@chromium.org> (raw)
According to the SMCCC spec[1](7.5.2 Discovery) the
ARM_SMCCC_ARCH_WORKAROUND_1 function id only returns 0, 1, and
SMCCC_RET_NOT_SUPPORTED.
0 is "workaround required and safe to call this function"
1 is "workaround not required but safe to call this function"
SMCCC_RET_NOT_SUPPORTED is "might be vulnerable or might not be, who knows, I give up!"
SMCCC_RET_NOT_SUPPORTED might as well mean "workaround required, except
calling this function may not work because it isn't implemented in some
cases". Wonderful. We map this SMC call to
0 is SPECTRE_MITIGATED
1 is SPECTRE_UNAFFECTED
SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE
For KVM hypercalls (hvc), we've implemented this function id to return
SMCCC_RET_NOT_SUPPORTED, 0, and SMCCC_RET_NOT_REQUIRED. One of those
isn't supposed to be there. Per the code we call
arm64_get_spectre_v2_state() to figure out what to return for this
feature discovery call.
0 is SPECTRE_MITIGATED
SMCCC_RET_NOT_REQUIRED is SPECTRE_UNAFFECTED
SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE
Let's clean this up so that KVM tells the guest this mapping:
0 is SPECTRE_MITIGATED
1 is SPECTRE_UNAFFECTED
SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE
Note: SMCCC_RET_NOT_AFFECTED is 1 but isn't part of the SMCCC spec
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org
Link: https://developer.arm.com/documentation/den0028/latest [1]
Fixes: c118bbb52743 ("arm64: KVM: Propagate full Spectre v2 workaround state to KVM guests")
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---
I see that before commit c118bbb52743 ("arm64: KVM: Propagate full
Spectre v2 workaround state to KVM guests") we had this mapping:
0 is SPECTRE_MITIGATED
SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE
so the return value '1' wasn't there then. Once the commit was merged we
introduced the notion of NOT_REQUIRED here when it shouldn't have been
introduced.
Changes from v2:
* Moved define to header file and used it
Changes from v1:
* Way longer commit text, more background (sorry)
* Dropped proton-pack part because it was wrong
* Rebased onto other patch accepted upstream
arch/arm64/kernel/proton-pack.c | 2 --
arch/arm64/kvm/hypercalls.c | 2 +-
include/linux/arm-smccc.h | 2 ++
3 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index 25f3c80b5ffe..c18eb7d41274 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -135,8 +135,6 @@ static enum mitigation_state spectre_v2_get_cpu_hw_mitigation_state(void)
return SPECTRE_VULNERABLE;
}
-#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED (1)
-
static enum mitigation_state spectre_v2_get_cpu_fw_mitigation_state(void)
{
int ret;
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index 9824025ccc5c..25ea4ecb6449 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -31,7 +31,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
val = SMCCC_RET_SUCCESS;
break;
case SPECTRE_UNAFFECTED:
- val = SMCCC_RET_NOT_REQUIRED;
+ val = SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED;
break;
}
break;
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index 15c706fb0a37..0e50ba3e88d7 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -86,6 +86,8 @@
ARM_SMCCC_SMC_32, \
0, 0x7fff)
+#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED 1
+
/* Paravirtualised time calls (defined by ARM DEN0057A) */
#define ARM_SMCCC_HV_PV_TIME_FEATURES \
ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \
base-commit: 66dd3474702aa98d5844367e1577cdad78ef7c65
--
Sent by a computer, using git, on the internet
next reply other threads:[~2020-10-23 15:47 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-23 15:47 Stephen Boyd [this message]
2020-10-26 13:25 ` [PATCH v3] KVM: arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesn't return SMCCC_RET_NOT_REQUIRED Will Deacon
2020-10-27 21:41 ` Stephen Boyd
2020-10-28 10:03 ` Marc Zyngier
2020-10-28 15:12 ` Will Deacon
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