From: Salil Mehta <salil.mehta@huawei.com>
To: Marc Zyngier <maz@kernel.org>, Oliver Upton <oliver.upton@linux.dev>
Cc: "kvmarm@lists.linux.dev" <kvmarm@lists.linux.dev>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
yuzenghui <yuzenghui@huawei.com>,
Sean Christopherson <seanjc@google.com>
Subject: RE: [PATCH v3 08/13] KVM: arm64: Add support for KVM_EXIT_HYPERCALL
Date: Thu, 18 May 2023 09:08:46 +0000 [thread overview]
Message-ID: <30eae0208b55463bb644c6700951d4b8@huawei.com> (raw)
In-Reply-To: <86ilcqkqrf.wl-maz@kernel.org>
Hi Marc,
> From: Marc Zyngier <maz@kernel.org>
> Sent: Thursday, May 18, 2023 9:06 AM
> To: Oliver Upton <oliver.upton@linux.dev>
> Cc: Salil Mehta <salil.mehta@huawei.com>; kvmarm@lists.linux.dev;
> kvm@vger.kernel.org; Paolo Bonzini <pbonzini@redhat.com>; James Morse
> <james.morse@arm.com>; Suzuki K Poulose <suzuki.poulose@arm.com>; yuzenghui
> <yuzenghui@huawei.com>; Sean Christopherson <seanjc@google.com>
> Subject: Re: [PATCH v3 08/13] KVM: arm64: Add support for
> KVM_EXIT_HYPERCALL
>
> On Wed, 17 May 2023 19:38:14 +0100,
> Oliver Upton <oliver.upton@linux.dev> wrote:
> >
> > Hi Salil,
> >
> > On Wed, May 17, 2023 at 06:00:18PM +0000, Salil Mehta wrote:
> >
> > [...]
> >
> > > > > Should we expose the ESR, or at least ESR_EL2.IL as an additional
> > > > > flag?
> > >
> > >
> > > I think we would need "Immediate value" of the ESR_EL2 register in the
> > > user-space/VMM to be able to construct the syndrome value. I cannot see
> > > where it is being sent?
> >
> > The immediate value is not exposed to userspace, although by definition
> > the immediate value must be zero. The SMCCC spec requires all compliant
> > calls to use an immediate of zero (DEN0028E 2.9).
> >
> > Is there a legitimate use case for hypercalls with a nonzero immediate?
> > They would no longer be considered SMCCC calls at that point, so they
> > wouldn't work with the new UAPI.
>
> I agree. The use of non-zero immediate has long been deprecated. I
> guess we should actually reject non-zero immediate for HVC just like
> we do for SMC.
Ok. Maybe I will hard code Immediate value as 0 to create a syndrome value
at the VMM/Qemu and will also put a note stating non-zero immediate for
HVC/SVC are not supported/deprecated.
> If there is an actual need for a non-zero immediate to be propagated
> to userspace (want to emulate Xen's infamous 'HVC #0xEA1'?), then this
> should be an extension to the current API.
Oh ok, then perhaps this new extension change should be simultaneously
committed to avoid breaking Xen?
Thanks
Salil
next prev parent reply other threads:[~2023-05-18 9:24 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-04 15:40 [PATCH v3 00/13] KVM: arm64: Userspace SMCCC call filtering Oliver Upton
2023-04-04 15:40 ` [PATCH v3 01/13] KVM: x86: Redefine 'longmode' as a flag for KVM_EXIT_HYPERCALL Oliver Upton
2023-04-04 15:40 ` [PATCH v3 02/13] KVM: arm64: Add a helper to check if a VM has ran once Oliver Upton
2023-04-04 15:40 ` [PATCH v3 03/13] KVM: arm64: Add vm fd device attribute accessors Oliver Upton
2023-04-04 15:40 ` [PATCH v3 04/13] KVM: arm64: Rename SMC/HVC call handler to reflect reality Oliver Upton
2023-04-04 15:40 ` [PATCH v3 05/13] KVM: arm64: Start handling SMCs from EL1 Oliver Upton
2023-04-04 15:40 ` [PATCH v3 06/13] KVM: arm64: Refactor hvc filtering to support different actions Oliver Upton
2023-04-04 15:40 ` [PATCH v3 07/13] KVM: arm64: Use a maple tree to represent the SMCCC filter Oliver Upton
2023-04-04 15:40 ` [PATCH v3 08/13] KVM: arm64: Add support for KVM_EXIT_HYPERCALL Oliver Upton
2023-04-05 7:35 ` Marc Zyngier
2023-04-05 11:59 ` Marc Zyngier
2023-04-05 15:30 ` Oliver Upton
2023-05-17 18:00 ` Salil Mehta
2023-05-17 18:38 ` Oliver Upton
2023-05-18 8:06 ` Marc Zyngier
2023-05-18 9:08 ` Salil Mehta [this message]
2023-05-18 9:42 ` Marc Zyngier
2023-05-18 12:16 ` Salil Mehta
2023-05-18 8:54 ` Salil Mehta
2023-04-04 15:40 ` [PATCH v3 09/13] KVM: arm64: Introduce support for userspace SMCCC filtering Oliver Upton
2023-04-04 15:40 ` [PATCH v3 10/13] KVM: arm64: Return NOT_SUPPORTED to guest for unknown PSCI version Oliver Upton
2023-04-04 15:40 ` [PATCH v3 11/13] KVM: arm64: Let errors from SMCCC emulation to reach userspace Oliver Upton
2023-04-04 15:40 ` [PATCH v3 12/13] KVM: selftests: Add a helper for SMCCC calls with SMC instruction Oliver Upton
2023-04-04 15:40 ` [PATCH v3 13/13] KVM: selftests: Add test for SMCCC filter Oliver Upton
2023-04-05 18:45 ` [PATCH v3 00/13] KVM: arm64: Userspace SMCCC call filtering Marc Zyngier
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