linux-kernel - Re: [PATCH 0/3] cxl/mbox: support background operation abort requests

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Message-ID: <vtj5cp6brmyvqut6xaxo3vfgnidvzwxr4kv6ofuiimcga5dyke@ts32khqtmexa>
Date: Wed, 23 Oct 2024 16:35:57 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: Ravis OpenSrc <Ravis.OpenSrc@...ron.com>
Cc: "dan.j.williams@...el.com" <dan.j.williams@...el.com>, 
	"dave.jiang@...el.com" <dave.jiang@...el.com>, "jonathan.cameron@...wei.com" <jonathan.cameron@...wei.com>, 
	"alison.schofield@...el.com" <alison.schofield@...el.com>, "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>, 
	"ira.weiny@...el.com" <ira.weiny@...el.com>, "fan.ni@...sung.com" <fan.ni@...sung.com>, 
	"a.manzanares@...sung.com" <a.manzanares@...sung.com>, Srinivasulu Opensrc <sthanneeru.opensrc@...ron.com>, 
	Eishan Mirakhur <emirakhur@...ron.com>, Ajay Joshi <ajayjoshi@...ron.com>, 
	Srinivasulu Thanneeru <sthanneeru@...ron.com>, "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] cxl/mbox: support background operation abort requests

On Wed, 23 Oct 2024, Ravis OpenSrc wrote:
>The one major functionality in our original proposal apart from implementing abort is
>
>Allowing background commands to be invoked from user space through the primary mailbox
>by ensuring only those background commands are enabled which also support request abort operation
>by checking their individual CEL details.

Is vendor-specific logs not something that can be done OoB?

If we are strictly talking about CEL details, yes this series could use that, and was
planning on adding it for an eventual v2 -- ie: why send the abort cmd at all if we
know the current one doesn't support it. But that is minutiae, for kernel bg commands.

But yeah, for your needs, the enabled cmds would need that filter.

Then with that, would adding something like the below address your needs and below
questions? Basically, if userspace is running a command, then the kernel comes in
and wants to run its own bg command, it will simply abort *anything* ongoing as a
last resort. And since we have no kernel-context about whatever is running at that
point, is *think* it is safe to assume it was user-initiated.

diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
index 7b0fad7f6c4d..bf0742546ea8 100644
--- a/drivers/cxl/pci.c
+++ b/drivers/cxl/pci.c
@@ -374,7 +374,7 @@ static bool cxl_try_to_cancel_background(struct cxl_mailbox *cxl_mbox)
		mds->security.sanitize_active = false;

		dev_dbg(cxlds->dev, "Sanitization operation aborted\n");
-	} else {
+	} else if (atomic_read_acquire(&cxl_mbox->poll_bgop)){
		/*
		 * Kick the poller and wait for it to be done - no one else
		 * can touch mbox regs. rcuwait_wake_up() provides full
@@ -403,7 +403,9 @@ static int cxl_pci_mbox_send(struct cxl_mailbox *cxl_mbox,
	 */
	if (cxl_is_background_cmd(cmd->opcode)) {
		if (mds->security.sanitize_active ||
-		    atomic_read_acquire(&cxl_mbox->poll_bgop)) {
+		    atomic_read_acquire(&cxl_mbox->poll_bgop) ||
+		    /* userspace-initiated ? */
+		    !cxl_mbox_background_done(cxlds)) {
			if (!cxl_try_to_cancel_background(cxl_mbox)) {
				mutex_unlock(&cxl_mbox->mbox_mutex);
				return -EBUSY;