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Wed, 21 Oct 2020 20:30:00 -0700 (PDT) Received: from smtp.gmail.com ([2620:15c:202:201:3e52:82ff:fe6c:83ab]) by smtp.gmail.com with ESMTPSA id p12sm297782pgm.29.2020.10.21.20.29.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Oct 2020 20:29:59 -0700 (PDT) From: Stephen Boyd To: Will Deacon , Catalin Marinas Subject: [PATCH v2] KVM: arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesn't return SMCCC_RET_NOT_REQUIRED Date: Wed, 21 Oct 2020 20:29:58 -0700 Message-Id: <20201022032958.265621-1-swboyd@chromium.org> X-Mailer: git-send-email 2.29.0.rc1.297.gfa9743e501-goog MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201021_233002_792199_82CE76E1 X-CRM114-Status: GOOD ( 17.72 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andre Przywara , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Steven Price , Marc Zyngier , linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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: Moving SMCCC_RET_NOT_AFFECTED to a header is left out of this patch as it would need to move from proton-pack.c which isn't in stable trees and the name isn't actually part of the SMCCC spec) Cc: Andre Przywara Cc: Steven Price Cc: Marc Zyngier 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 --- 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 v1: * Way longer commit text, more background (sorry) * Dropped proton-pack part because it was wrong * Rebased onto other patch accepted upstream arch/arm64/kvm/hypercalls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) base-commit: 66dd3474702aa98d5844367e1577cdad78ef7c65 diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c index 9824025ccc5c..6a62312d7813 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 = 1; break; } break;