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From: Sean Christopherson <seanjc@google.com>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kvmarm@lists.linux.dev, Akihiko Odaki <akihiko.odaki@daynix.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Raghavendra Rao Ananta <rananta@google.com>,
	linux-arm-kernel@lists.infradead.org,
	Salil Mehta <salil.mehta@huawei.com>
Subject: Re: [RFC PATCH v2 5/6] KVM: arm64: Add support for KVM_EXIT_HYPERCALL
Date: Mon, 13 Feb 2023 16:01:29 +0000	[thread overview]
Message-ID: <Y+pe2T2uK2efUNve@google.com> (raw)
In-Reply-To: <20230211013759.3556016-6-oliver.upton@linux.dev>

On Sat, Feb 11, 2023, Oliver Upton wrote:
> Finally, we need a flag to let userspace know what conduit instruction
> was used (i.e. SMC vs. HVC). Redefine the remaining padding in
> kvm_run::hypercall to accomplish this. Let's all take a moment
> to admire the flowers and see how 'longmode' tied up a full u32 in the
> UAPI. Weep.

I don't think it has to, at least not for other architectures.  No other arch
currently supports KVM_EXIT_HYPERCALL, so breakage is extremely unlikely.  E.g.
we can likely get away with this, and then just have x86 add new flags at bit 32.

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 55155e262646..7d3ad820d55c 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -341,8 +341,14 @@ struct kvm_run {
                        __u64 nr;
                        __u64 args[6];
                        __u64 ret;
-                       __u32 longmode;
-                       __u32 pad;
+                       union {
+                               /*
+                                * Long Mode, a.k.a. 64-bit mode, takes up the
+                                * first 32 flags on x86 (historical sludge).
+                                */
+                               __u32 longmode;
+                               __u64 flags;
+                       };
                } hypercall;
                /* KVM_EXIT_TPR_ACCESS */
                struct {
 

WARNING: multiple messages have this Message-ID (diff)
From: Sean Christopherson <seanjc@google.com>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kvmarm@lists.linux.dev, Akihiko Odaki <akihiko.odaki@daynix.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Raghavendra Rao Ananta <rananta@google.com>,
	linux-arm-kernel@lists.infradead.org,
	Salil Mehta <salil.mehta@huawei.com>
Subject: Re: [RFC PATCH v2 5/6] KVM: arm64: Add support for KVM_EXIT_HYPERCALL
Date: Mon, 13 Feb 2023 16:01:29 +0000	[thread overview]
Message-ID: <Y+pe2T2uK2efUNve@google.com> (raw)
In-Reply-To: <20230211013759.3556016-6-oliver.upton@linux.dev>

On Sat, Feb 11, 2023, Oliver Upton wrote:
> Finally, we need a flag to let userspace know what conduit instruction
> was used (i.e. SMC vs. HVC). Redefine the remaining padding in
> kvm_run::hypercall to accomplish this. Let's all take a moment
> to admire the flowers and see how 'longmode' tied up a full u32 in the
> UAPI. Weep.

I don't think it has to, at least not for other architectures.  No other arch
currently supports KVM_EXIT_HYPERCALL, so breakage is extremely unlikely.  E.g.
we can likely get away with this, and then just have x86 add new flags at bit 32.

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 55155e262646..7d3ad820d55c 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -341,8 +341,14 @@ struct kvm_run {
                        __u64 nr;
                        __u64 args[6];
                        __u64 ret;
-                       __u32 longmode;
-                       __u32 pad;
+                       union {
+                               /*
+                                * Long Mode, a.k.a. 64-bit mode, takes up the
+                                * first 32 flags on x86 (historical sludge).
+                                */
+                               __u32 longmode;
+                               __u64 flags;
+                       };
                } hypercall;
                /* KVM_EXIT_TPR_ACCESS */
                struct {
 

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  reply	other threads:[~2023-02-13 16:01 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-11  1:37 [RFC PATCH v2 0/6] KVM: arm64: Userspace SMCCC call filtering Oliver Upton
2023-02-11  1:37 ` Oliver Upton
2023-02-11  1:37 ` [RFC PATCH v2 1/6] KVM: arm64: Add a helper to check if a VM has ran once Oliver Upton
2023-02-11  1:37   ` Oliver Upton
2023-02-13 15:36   ` Sean Christopherson
2023-02-13 15:36     ` Sean Christopherson
2023-02-13 15:49     ` Marc Zyngier
2023-02-13 15:49       ` Marc Zyngier
2023-02-11  1:37 ` [RFC PATCH v2 2/6] KVM: arm64: Add vm fd device attribute accessors Oliver Upton
2023-02-11  1:37   ` Oliver Upton
2023-02-11  1:37 ` [RFC PATCH v2 3/6] KVM: arm64: Refactor hvc filtering to support different actions Oliver Upton
2023-02-11  1:37   ` Oliver Upton
2023-02-11  1:37 ` [RFC PATCH v2 4/6] KVM: arm64: Use a maple tree to represent the SMCCC filter Oliver Upton
2023-02-11  1:37   ` Oliver Upton
2023-02-11  1:37 ` [RFC PATCH v2 5/6] KVM: arm64: Add support for KVM_EXIT_HYPERCALL Oliver Upton
2023-02-11  1:37   ` Oliver Upton
2023-02-13 16:01   ` Sean Christopherson [this message]
2023-02-13 16:01     ` Sean Christopherson
2023-02-13 19:24     ` Oliver Upton
2023-02-13 19:24       ` Oliver Upton
2023-02-24 15:12   ` James Morse
2023-02-24 15:12     ` James Morse
2023-02-24 21:42     ` Oliver Upton
2023-02-24 21:42       ` Oliver Upton
2023-02-11  1:37 ` [RFC PATCH v2 6/6] KVM: arm64: Indroduce support for userspace SMCCC filtering Oliver Upton
2023-02-11  1:37   ` Oliver Upton
2023-02-17 18:35   ` Oliver Upton
2023-02-17 18:35     ` Oliver Upton
2023-02-24 15:12 ` [RFC PATCH v2 0/6] KVM: arm64: Userspace SMCCC call filtering James Morse
2023-02-24 15:12   ` James Morse
2023-02-24 21:32   ` Oliver Upton
2023-02-24 21:32     ` Oliver Upton

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