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Subject: Re: [pve-devel] [PATCH qemu-server v8 1/3] add C program to get
hardware capabilities from CPUID
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On Thu Apr 25, 2024 at 1:24 PM CEST, Markus Frank wrote:
> Implement a systemd service that runs a C program that extracts AMD
> SEV hardware information such as reduced-phys-bios and cbitpos from
> CPUID at boot time, looks if SEV, SEV-ES & SEV-SNP are enabled, and
> outputs these details as JSON to /run/qemu-server/hw-params.json.
>
> This programm can also be used to read and save other hardware
> information at boot time.
>
> Signed-off-by: Markus Frank <m.frank@proxmox.com>
> Co-authored-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
> ---
> v8:
> * renamed query-machine-params to query-machine-capabilities
>
> v7:
> * renamed amd-sev-support to query-machine-params
> * mv /run/amd-sev-params to /run/qemu-server/hw-params.json
> * add "mkdir /run/qemu-server" to ensure that the directory exists
> * moved json content to amd-sev property inside a bigger json
> so that other hardware parameters could also be read at boot time and
> included in this json file.
>
> Makefile | 1 +
> query-machine-capabilities/Makefile | 21 +++++++
> .../query-machine-capabilities.c | 55 +++++++++++++++++++
> .../query-machine-capabilities.service | 12 ++++
> 4 files changed, 89 insertions(+)
> create mode 100644 query-machine-capabilities/Makefile
> create mode 100644 query-machine-capabilities/query-machine-capabilities.c
> create mode 100644 query-machine-capabilities/query-machine-capabilities.service
>
> diff --git a/Makefile b/Makefile
> index 133468d..ed67fe0 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -65,6 +65,7 @@ install: $(PKGSOURCES)
> install -m 0644 -D bootsplash.jpg $(DESTDIR)/usr/share/$(PACKAGE)
> $(MAKE) -C PVE install
> $(MAKE) -C qmeventd install
> + $(MAKE) -C query-machine-capabilities install
> $(MAKE) -C qemu-configs install
> $(MAKE) -C vm-network-scripts install
> install -m 0755 qm $(DESTDIR)$(SBINDIR)
> diff --git a/query-machine-capabilities/Makefile b/query-machine-capabilities/Makefile
> new file mode 100644
> index 0000000..c5f6348
> --- /dev/null
> +++ b/query-machine-capabilities/Makefile
> @@ -0,0 +1,21 @@
> +DESTDIR=
> +PREFIX=/usr
> +SBINDIR=${PREFIX}/libexec/qemu-server
> +SERVICEDIR=/lib/systemd/system
> +
> +CC ?= gcc
> +CFLAGS += -O2 -fanalyzer -Werror -Wall -Wextra -Wpedantic -Wtype-limits -Wl,-z,relro -std=gnu11
> +
> +query-machine-capabilities: query-machine-capabilities.c
> + $(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)
> +
> +.PHONY: install
> +install: query-machine-capabilities
> + install -d ${DESTDIR}/${SBINDIR}
> + install -d ${DESTDIR}${SERVICEDIR}
> + install -m 0644 query-machine-capabilities.service ${DESTDIR}${SERVICEDIR}
> + install -m 0755 query-machine-capabilities ${DESTDIR}${SBINDIR}
> +
> +.PHONY: clean
> +clean:
> + rm -f query-machine-capabilities
> diff --git a/query-machine-capabilities/query-machine-capabilities.c b/query-machine-capabilities/query-machine-capabilities.c
> new file mode 100644
> index 0000000..f4a9f9f
> --- /dev/null
> +++ b/query-machine-capabilities/query-machine-capabilities.c
> @@ -0,0 +1,55 @@
> +#include <stdio.h>
> +#include <stdint.h>
> +#include <stdbool.h>
> +#include <sys/stat.h>
> +#include <sys/types.h>
> +
> +int main() {
> + uint32_t eax, ebx, ecx, edx;
> +
> + // query Encrypted Memory Capabilities, see:
> + // https://en.wikipedia.org/wiki/CPUID#EAX=8000001Fh:_Encrypted_Memory_Capabilities
> + uint32_t query_function = 0x8000001F;
> + asm volatile("cpuid"
> + : "=a"(eax), "=b"(ebx), "=c"(ecx), "=d"(edx)
> + : "0"(query_function)
> + );
> +
> + bool sev_support = (eax & (1<<1)) != 0;
> + bool sev_es_support = (eax & (1<<3)) != 0;
> + bool sev_snp_support = (eax & (1<<4)) != 0;
> +
> + uint8_t cbitpos = ebx & 0x3f;
> + uint8_t reduced_phys_bits = (ebx >> 6) & 0x3f;
> +
> + FILE *file;
> + char filename[] = "/run/qemu-server/host-hw-capabilities.json";
> +
> + mkdir("/run/qemu-server/", 0755);
> +
wouldn't it make sense to check whether this call succeeded too like you
do for the `fopen` below? also might be nice to use `strerror` and
handle `errno` in those cases too.
> + file = fopen(filename, "w");
> + if (file == NULL) {
> + perror("Error opening file");
> + return 1;
> + }
> +
> + fprintf(file,
> + "{"
> + " \"amd-sev\": {"
> + " \"cbitpos\": %u,"
> + " \"reduced-phys-bits\": %u,"
> + " \"sev-support\": %s,"
> + " \"sev-support-es\": %s,"
> + " \"sev-support-snp\": %s"
> + " }"
> + " }\n",
> + cbitpos,
> + reduced_phys_bits,
> + sev_support ? "true" : "false",
> + sev_es_support ? "true" : "false",
> + sev_snp_support ? "true" : "false"
> + );
> +
> + fclose(file);
> + return 0;
> +}
> diff --git a/query-machine-capabilities/query-machine-capabilities.service b/query-machine-capabilities/query-machine-capabilities.service
> new file mode 100644
> index 0000000..f926074
> --- /dev/null
> +++ b/query-machine-capabilities/query-machine-capabilities.service
> @@ -0,0 +1,12 @@
> +[Unit]
> +Description=read AMD SEV parameters
> +RequiresMountsFor=/run
> +Before=pve-ha-lrm.service
> +Before=pve-guests.service
> +
> +[Service]
> +ExecStart=/usr/libexec/qemu-server/query-machine-capabilities
> +Type=oneshot
> +
> +[Install]
> +WantedBy=multi-user.target
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