linux-kernel - Re: [PATCH v0 5/6] x86/hyperv: Implement hypervisor ram collection into vmcore

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aL8Cfsl3Vaeuw-QI@skinsburskii.localdomain>
Date: Mon, 8 Sep 2025 09:21:18 -0700
From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
To: Mukesh Rathor <mrathor@...ux.microsoft.com>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, kys@...rosoft.com,
	haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
	arnd@...db.de
Subject: Re: [PATCH v0 5/6] x86/hyperv: Implement hypervisor ram collection
 into vmcore

On Wed, Sep 03, 2025 at 07:10:16PM -0700, Mukesh Rathor wrote:
> This commit introduces a new file to enable collection of hypervisor ram
> into the vmcore collected by linux. By default, the hypervisor ram is locked,
> ie, protected via hw page table. Hyper-V implements a disable hypercall which
> essentially devirtualizes the system on the fly. This mechanism makes the
> hypervisor ram accessible to linux without any extra work because it is
> already mapped into linux address space. Details of the implementation
> are available in the file prologue.
> 
> Signed-off-by: Mukesh Rathor <mrathor@...ux.microsoft.com>
> ---
>  arch/x86/hyperv/hv_crash.c | 618 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 618 insertions(+)
>  create mode 100644 arch/x86/hyperv/hv_crash.c
> 
> diff --git a/arch/x86/hyperv/hv_crash.c b/arch/x86/hyperv/hv_crash.c
> new file mode 100644
> index 000000000000..50c54d39f0e2
> --- /dev/null
> +++ b/arch/x86/hyperv/hv_crash.c
> +

<snip>

> +/*
> + * generic nmi callback handler: could be called without any crash also.
> + *  hv crash: hypervisor injects nmi's into all cpus
> + *  lx crash: panicing cpu sends nmi to all but self via crash_stop_other_cpus
> + */
> +static int hv_crash_nmi_local(unsigned int cmd, struct pt_regs *regs)
> +{
> +	int ccpu = smp_processor_id();
> +
> +	if (!hv_has_crashed && hv_cda && hv_cda->cda_valid)
> +		hv_has_crashed = 1;
> +
> +	if (!hv_has_crashed && !lx_has_crashed)
> +		return NMI_DONE;	/* ignore the nmi */
> +
> +	if (hv_has_crashed && !hv_crash_enabled) {
> +		if (ccpu == 0) {
> +			pr_emerg("Hyper-V: core collect not setup. Reboot\n");
> +			native_wrmsrq(HV_X64_MSR_RESET, 1);	/* reboot */
> +		} else
> +			for (;;)
> +				cpu_relax();
> +	}
> +
> +	crash_nmi_callback(regs);
> +	return NMI_DONE;
> +}

One more thing.
It looks like the function above goes through the new logic even when
hypervisor is intact and there is no crash kernel loaded.
This is redundant and it should rather return back to the existent
generic kernel panic logic.

Stanislav