Re: [PATCH v1 2/4] x86/vmware: Add the vmware_record_panic_msg sysctl

[Joel Granados]

On Tue, Sep 08, 2026 at 02:07:14PM -0400, Zack Rusin wrote:
> Full panic text is useful on ordinary guests. Encrypted guests should
> export it only when an administrator opts in. Reporting a crash does not
> require transferring the log.
> 
> Enable panic recording by default for ordinary VMware guests and disable
> it when guest memory encryption is active. Expose the policy as the
> boolean kernel.vmware_record_panic_msg sysctl and document that it
> controls only the vmware.log transfer.
> 
> Register the sysctl only after the panic buffer and dumper are ready, and
> only when sysctl support is built. A registration failure leaves the
> internal default in force.
> 
> Signed-off-by: Zack Rusin <zack.rusin@xxxxxxxxxxxx>
> ---
>  Documentation/admin-guide/sysctl/kernel.rst | 14 +++++++++++++
>  arch/x86/kernel/cpu/vmware.c                | 23 +++++++++++++++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index b6328cd0f43e..4577e935ddcf 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -1690,6 +1690,20 @@ entry will default to 2 instead of 0.
>  = =============================================================
>  
>  
> +vmware_record_panic_msg
> +=======================
> +
> +Controls whether panic kmsg data is written to the host's ``vmware.log``.
> +This setting does not control the separate VMware guest-crash event.
> +
> += ==============================================================
> +0 Do not write panic kmsg data to ``vmware.log``. This is the
> +  default for encrypted guests.
> +1 Write panic kmsg data to ``vmware.log``. This is the default for
> +  ordinary guests.
> += ==============================================================

This seems like it can be represented in a boolean value. Any reason why
you did not use proc_dobool for your handler? Would it make sense to
have vmware_record_panic_msg as a boolean?

Best

> +
> +
>  warn_limit
>  ==========
>  
> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
> index bf59653d6e07..3848811550e9 100644
> --- a/arch/x86/kernel/cpu/vmware.c
> +++ b/arch/x86/kernel/cpu/vmware.c
> @@ -31,6 +31,7 @@
>  #include <linux/efi.h>
>  #include <linux/reboot.h>
>  #include <linux/static_call.h>
> +#include <linux/sysctl.h>
>  #include <linux/wordpart.h>
>  #include <linux/sched/cputime.h>
>  #include <asm/div64.h>
> @@ -255,6 +256,19 @@ static int vmware_log_rpc(const char *buffer, size_t length)
>  }
>  
>  static struct page *vmware_panic_page;
> +static int vmware_record_panic_msg;
> +
> +static const struct ctl_table vmware_panic_sysctls[] = {
> +	{
> +		.procname	= "vmware_record_panic_msg",
> +		.data		= &vmware_record_panic_msg,
> +		.maxlen		= sizeof(vmware_record_panic_msg),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= SYSCTL_ZERO,
> +		.extra2		= SYSCTL_ONE,
> +	},
> +};
>  
>  static void vmware_panic_log_dump(struct kmsg_dumper *dumper,
>  				  struct kmsg_dump_detail *detail)
> @@ -263,6 +277,9 @@ static void vmware_panic_log_dump(struct kmsg_dumper *dumper,
>  	char *buffer = page_address(vmware_panic_page);
>  	size_t length = 0;
>  
> +	if (!READ_ONCE(vmware_record_panic_msg))
> +		return;
> +
>  	memcpy(buffer, VMWARE_LOG_PREFIX, VMWARE_LOG_PREFIX_LEN);
>  	kmsg_dump_rewind(&iter);
>  	(void)kmsg_dump_get_buffer(&iter, true,
> @@ -283,6 +300,9 @@ static int __init vmware_panic_log_init(void)
>  	if (!hypervisor_is_type(X86_HYPER_VMWARE))
>  		return 0;
>  
> +	vmware_record_panic_msg =
> +		!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT);
> +
>  	vmware_panic_page = alloc_page(GFP_KERNEL);
>  	if (!vmware_panic_page) {
>  		pr_err("failed to allocate panic log buffer\n");
> @@ -295,6 +315,9 @@ static int __init vmware_panic_log_init(void)
>  		__free_page(vmware_panic_page);
>  		vmware_panic_page = NULL;
>  	}
> +	if (vmware_panic_page && IS_ENABLED(CONFIG_SYSCTL) &&
> +	    !register_sysctl("kernel", vmware_panic_sysctls))
> +		pr_err("failed to register panic log sysctl\n");
>  
>  	return 0;
>  }
> -- 
> 2.53.0
>

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