From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: Re: [PATCH v3 24/28] arm64/sve: KVM: Hide SVE from CPU features exposed to guests Date: Tue, 17 Oct 2017 06:58:16 -0700 Message-ID: <20171017135816.GF5886@lvm> References: <1507660725-7986-1-git-send-email-Dave.Martin@arm.com> <1507660725-7986-25-git-send-email-Dave.Martin@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-path: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Content-Disposition: inline In-Reply-To: <1507660725-7986-25-git-send-email-Dave.Martin@arm.com> To: Dave Martin Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, Okamoto Takayuki , libc-alpha@sourceware.org, Ard Biesheuvel , Szabolcs Nagy , Catalin Marinas , Will Deacon , Marc Zyngier , Richard Sandiford , kvmarm@lists.cs.columbia.edu List-Id: linux-arch.vger.kernel.org On Tue, Oct 10, 2017 at 07:38:41PM +0100, Dave Martin wrote: > KVM guests cannot currently use SVE, because SVE is always > configured to trap to EL2. > > However, a guest that sees SVE reported as present in > ID_AA64PFR0_EL1 may legitimately expect that SVE works and try to > use it. Instead of working, the guest will receive an injected > undef exception, which may cause the guest to oops or go into a > spin. > > To avoid misleading the guest into believing that SVE will work, > this patch masks out the SVE field from ID_AA64PFR0_EL1 when a > guest attempts to read this register. No support is explicitly > added for ID_AA64ZFR0_EL1 either, so that is still emulated as > reading as zero, which is consistent with SVE not being > implemented. > > This is a temporary measure, and will be removed in a later series > when full KVM support for SVE is implemented. > > Signed-off-by: Dave Martin > Reviewed-by: Alex Bennée > Cc: Marc Zyngier > --- > arch/arm64/kvm/sys_regs.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index b1f7552..a0ee9b0 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -23,6 +23,7 @@ > #include > #include > #include > +#include > #include > > #include > @@ -897,8 +898,17 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz) > { > u32 id = sys_reg((u32)r->Op0, (u32)r->Op1, > (u32)r->CRn, (u32)r->CRm, (u32)r->Op2); > + u64 val = raz ? 0 : read_sanitised_ftr_reg(id); > > - return raz ? 0 : read_sanitised_ftr_reg(id); > + if (id == SYS_ID_AA64PFR0_EL1) { > + if (val & (0xfUL << ID_AA64PFR0_SVE_SHIFT)) > + pr_err_once("kvm [%i]: SVE unsupported for guests, suppressing\n", > + task_pid_nr(current)); nit: does this really qualify as an error print? > + > + val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT); > + } > + > + return val; > } > > /* cpufeature ID register access trap handlers */ > -- > 2.1.4 > Otherwise: Acked-by: Christoffer Dall From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f43.google.com ([74.125.82.43]:52013 "EHLO mail-wm0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752505AbdJQN6T (ORCPT ); Tue, 17 Oct 2017 09:58:19 -0400 Received: by mail-wm0-f43.google.com with SMTP id f4so4174147wme.0 for ; Tue, 17 Oct 2017 06:58:18 -0700 (PDT) Date: Tue, 17 Oct 2017 06:58:16 -0700 From: Christoffer Dall Subject: Re: [PATCH v3 24/28] arm64/sve: KVM: Hide SVE from CPU features exposed to guests Message-ID: <20171017135816.GF5886@lvm> References: <1507660725-7986-1-git-send-email-Dave.Martin@arm.com> <1507660725-7986-25-git-send-email-Dave.Martin@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1507660725-7986-25-git-send-email-Dave.Martin@arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Dave Martin Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, Okamoto Takayuki , libc-alpha@sourceware.org, Ard Biesheuvel , Szabolcs Nagy , Catalin Marinas , Will Deacon , Marc Zyngier , Richard Sandiford , kvmarm@lists.cs.columbia.edu Message-ID: <20171017135816.BFUSe3YMoZGbSI-km0YaO5UHDln5ple10iIFW0CsHq4@z> On Tue, Oct 10, 2017 at 07:38:41PM +0100, Dave Martin wrote: > KVM guests cannot currently use SVE, because SVE is always > configured to trap to EL2. > > However, a guest that sees SVE reported as present in > ID_AA64PFR0_EL1 may legitimately expect that SVE works and try to > use it. Instead of working, the guest will receive an injected > undef exception, which may cause the guest to oops or go into a > spin. > > To avoid misleading the guest into believing that SVE will work, > this patch masks out the SVE field from ID_AA64PFR0_EL1 when a > guest attempts to read this register. No support is explicitly > added for ID_AA64ZFR0_EL1 either, so that is still emulated as > reading as zero, which is consistent with SVE not being > implemented. > > This is a temporary measure, and will be removed in a later series > when full KVM support for SVE is implemented. > > Signed-off-by: Dave Martin > Reviewed-by: Alex Bennée > Cc: Marc Zyngier > --- > arch/arm64/kvm/sys_regs.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index b1f7552..a0ee9b0 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -23,6 +23,7 @@ > #include > #include > #include > +#include > #include > > #include > @@ -897,8 +898,17 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz) > { > u32 id = sys_reg((u32)r->Op0, (u32)r->Op1, > (u32)r->CRn, (u32)r->CRm, (u32)r->Op2); > + u64 val = raz ? 0 : read_sanitised_ftr_reg(id); > > - return raz ? 0 : read_sanitised_ftr_reg(id); > + if (id == SYS_ID_AA64PFR0_EL1) { > + if (val & (0xfUL << ID_AA64PFR0_SVE_SHIFT)) > + pr_err_once("kvm [%i]: SVE unsupported for guests, suppressing\n", > + task_pid_nr(current)); nit: does this really qualify as an error print? > + > + val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT); > + } > + > + return val; > } > > /* cpufeature ID register access trap handlers */ > -- > 2.1.4 > Otherwise: Acked-by: Christoffer Dall