linux-kernel - Re: [PATCH v8 2/2] Drivers: hv: Introduce mshv

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <aO0I2va2HQ6mA-u0@google.com>
Date: Mon, 13 Oct 2025 07:12:42 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Naman Jain <namjain@...ux.microsoft.com>
Cc: "K . Y . Srinivasan" <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, 
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H . Peter Anvin" <hpa@...or.com>, 
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org, 
	Mukesh Rathor <mrathor@...ux.microsoft.com>, 
	Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>, 
	Nuno Das Neves <nunodasneves@...ux.microsoft.com>, Peter Zijlstra <peterz@...radead.org>, 
	Paolo Bonzini <pbonzini@...hat.com>, Michael Kelley <mhklinux@...look.com>, 
	Christoph Hellwig <hch@...radead.org>, Saurabh Sengar <ssengar@...ux.microsoft.com>, 
	ALOK TIWARI <alok.a.tiwari@...cle.com>
Subject: Re: [PATCH v8 2/2] Drivers: hv: Introduce mshv_vtl driver

On Mon, Oct 13, 2025, Naman Jain wrote:
> +static int mshv_vtl_ioctl_return_to_lower_vtl(void)
> +{
> +	preempt_disable();
> +	for (;;) {
> +		u32 cancel;
> +		unsigned long irq_flags;
> +		struct hv_vp_assist_page *hvp;
> +		int ret;
> +
> +		local_irq_save(irq_flags);
> +		cancel = READ_ONCE(mshv_vtl_this_run()->cancel);
> +		if (cancel)
> +			current_thread_info()->flags |= _TIF_SIGPENDING;

There's no need to force SIGPENDING, this code can return directly if cancel is
set[1].  And then you can wait to disable IRQs until after handling pending work,
and thus avoid having to immediately re-enable IRQs[2].

[1] https://lore.kernel.org/all/20250828000156.23389-3-seanjc@google.com
[2] https://lore.kernel.org/all/20250828000156.23389-4-seanjc@google.com

> +
> +		if (unlikely(cancel) || __xfer_to_guest_mode_work_pending()) {
> +			local_irq_restore(irq_flags);
> +			preempt_enable();
> +			ret = xfer_to_guest_mode_handle_work();
> +			if (ret)
> +				return ret;
> +			preempt_disable();
> +			continue;
> +		}
> +
> +		mshv_vtl_return(&mshv_vtl_this_run()->cpu_context);
> +		local_irq_restore(irq_flags);
> +
> +		hvp = hv_vp_assist_page[smp_processor_id()];
> +		this_cpu_inc(num_vtl0_transitions);
> +		switch (hvp->vtl_entry_reason) {
> +		case MSHV_ENTRY_REASON_INTERRUPT:
> +			if (!mshv_vsm_capabilities.intercept_page_available &&
> +			    likely(!mshv_vtl_process_intercept()))
> +				goto done;
> +			break;
> +
> +		case MSHV_ENTRY_REASON_INTERCEPT:
> +			WARN_ON(!mshv_vsm_capabilities.intercept_page_available);
> +			memcpy(mshv_vtl_this_run()->exit_message, hvp->intercept_message,
> +			       sizeof(hvp->intercept_message));
> +			goto done;
> +
> +		default:
> +			panic("unknown entry reason: %d", hvp->vtl_entry_reason);
> +		}
> +	}
> +
> +done:
> +	preempt_enable();
> +
> +	return 0;
> +}