Re: [PATCH v13 03/24] virt: gunyah: Add hypercalls to identify Gunyah

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On 5/9/23 3:47 PM, Elliot Berman wrote:
Add hypercalls to identify when Linux is running a virtual machine under
Gunyah.

There are two calls to help identify Gunyah:

1. gh_hypercall_get_uid() returns a UID when running under a Gunyah
    hypervisor.
2. gh_hypercall_hyp_identify() returns build information and a set of
    feature flags that are supported by Gunyah.

Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx>

I have a suggestion below.  But whether or not you choose to
incorporate it:

Reviewed-by: Alex Elder <elder@xxxxxxxxxx>

---
  arch/arm64/Kbuild                    |  1 +
  arch/arm64/gunyah/Makefile           |  3 ++
  arch/arm64/gunyah/gunyah_hypercall.c | 56 ++++++++++++++++++++++++++++
  drivers/virt/Kconfig                 |  2 +
  drivers/virt/gunyah/Kconfig          | 13 +++++++
  include/linux/gunyah.h               | 31 +++++++++++++++
  6 files changed, 106 insertions(+)
  create mode 100644 arch/arm64/gunyah/Makefile
  create mode 100644 arch/arm64/gunyah/gunyah_hypercall.c
  create mode 100644 drivers/virt/gunyah/Kconfig

diff --git a/arch/arm64/Kbuild b/arch/arm64/Kbuild
index 5bfbf7d79c99..e4847ba0e3c9 100644
--- a/arch/arm64/Kbuild
+++ b/arch/arm64/Kbuild
@@ -3,6 +3,7 @@ obj-y			+= kernel/ mm/ net/
  obj-$(CONFIG_KVM)	+= kvm/
  obj-$(CONFIG_XEN)	+= xen/
  obj-$(subst m,y,$(CONFIG_HYPERV))	+= hyperv/
+obj-$(CONFIG_GUNYAH)	+= gunyah/
  obj-$(CONFIG_CRYPTO)	+= crypto/
# for cleaning
diff --git a/arch/arm64/gunyah/Makefile b/arch/arm64/gunyah/Makefile
new file mode 100644
index 000000000000..84f1e38cafb1
--- /dev/null
+++ b/arch/arm64/gunyah/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_GUNYAH) += gunyah_hypercall.o
diff --git a/arch/arm64/gunyah/gunyah_hypercall.c b/arch/arm64/gunyah/gunyah_hypercall.c
new file mode 100644
index 000000000000..2166d5dab869
--- /dev/null
+++ b/arch/arm64/gunyah/gunyah_hypercall.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/module.h>
+#include <linux/gunyah.h>
+#include <linux/uuid.h>
+
+/* {c1d58fcd-a453-5fdb-9265-ce36673d5f14} */
+static const uuid_t GUNYAH_UUID =
+	UUID_INIT(0xc1d58fcd, 0xa453, 0x5fdb, 0x92, 0x65, 0xce, 0x36, 0x67, 0x3d, 0x5f, 0x14);
+
+bool arch_is_gh_guest(void)
+{
+	struct arm_smccc_res res;
+	uuid_t uuid;
+
+	arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
+
+	((u32 *)&uuid.b[0])[0] = lower_32_bits(res.a0);
+	((u32 *)&uuid.b[0])[1] = lower_32_bits(res.a1);
+	((u32 *)&uuid.b[0])[2] = lower_32_bits(res.a2);
+	((u32 *)&uuid.b[0])[3] = lower_32_bits(res.a3);

I think I'd rather see this more like:

	u32	*up = (u32 *)&uuid.b;

	/* The lower bytes of the four result fields encode the UUID */
	*up++ = lower_32_bits(res.a0);
	*up++ = lower_32_bits(res.a1);
	*up++ = lower_32_bits(res.a2);
	*up = lower_32_bits(res.a3);

Basically I think casting the assigned-to value makes things
harder to read.  So doing that cast just once seems simpler.
But it's not a big deal.

+
+	return uuid_equal(&uuid, &GUNYAH_UUID);
+}
+EXPORT_SYMBOL_GPL(arch_is_gh_guest);

. . .



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