Date:   Fri, 17 Mar 2023 17:30:23 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Eric DeVolder <eric.devolder@oracle.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, vgoyal@redhat.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com,
        robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com,
        sourabhjain@linux.ibm.com, konrad.wilk@oracle.com,
        boris.ostrovsky@oracle.com
Subject: Re: [PATCH v19 2/7] crash: add generic infrastructure for crash
 hotplug support
Message-ID: <ZBQzLxpLPcyhrDoF@MiWiFi-R3L-srv>
References: <20230306162228.8277-1-eric.devolder@oracle.com>
 <20230306162228.8277-3-eric.devolder@oracle.com>
 <ZBLrTl3UHYa1FV2S@MiWiFi-R3L-srv>
 <cab057d8-98d8-a72a-8b61-8a01a0f088e7@oracle.com>
 <cae43a11-b270-a5d6-7464-d92651c67c4a@oracle.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <cae43a11-b270-a5d6-7464-d92651c67c4a@oracle.com>
Precedence: bulk

On 03/16/23 at 10:47am, Eric DeVolder wrote:
> 
> 
> On 3/16/23 09:44, Eric DeVolder wrote:
> > 
> > 
> > On 3/16/23 05:11, Baoquan He wrote:
> > > On 03/06/23 at 11:22am, Eric DeVolder wrote:
> > > ......
> > > > +static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
> > > > +{
> > > > +??? /* Obtain lock while changing crash information */
> > > > +??? if (kexec_trylock()) {
> > > > +
> > > > +??????? /* Check kdump is loaded */
> > > > +??????? if (kexec_crash_image) {
> > > > +??????????? struct kimage *image = kexec_crash_image;
> > > > +
> > > > +??????????? if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
> > > > +??????????????? hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
> > > > +??????????????? pr_debug("hp_action %u, cpu %u\n", hp_action, cpu);
> > > > +??????????? else
> > > > +??????????????? pr_debug("hp_action %u\n", hp_action);
> > > > +
> > > > +??????????? /*
> > > > +???????????? * When the struct kimage is allocated, the elfcorehdr_index
> > > > +???????????? * is set to -1. Find the segment containing the elfcorehdr,
> > > > +???????????? * if not already found. This works for both the kexec_load
> > > > +???????????? * and kexec_file_load paths.
> > > > +???????????? */
> > > > +??????????? if (image->elfcorehdr_index < 0) {
> > > > +??????????????? unsigned long mem;
> > > > +??????????????? unsigned char *ptr;
> > > > +??????????????? unsigned int n;
> > > > +
> > > > +??????????????? for (n = 0; n < image->nr_segments; n++) {
> > > > +??????????????????? mem = image->segment[n].mem;
> > > > +??????????????????? ptr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
> > > > +??????????????????? if (ptr) {
> > > > +??????????????????????? /* The segment containing elfcorehdr */
> > > > +??????????????????????? if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
> > > > +??????????????????????????? image->elfcorehdr_index = (int)n;
> > > > +??????????????????????? }
> > > > +??????????????????????? kunmap_local(ptr);
> > > > +??????????????????? }
> > > > +??????????????? }
> > > > +??????????? }
> > > > +
> > > > +??????????? if (image->elfcorehdr_index < 0) {
> > > > +??????????????? pr_err("unable to locate elfcorehdr segment");
> > > > +??????????????? goto out;
> > > > +??????????? }
> > > > +
> > > > +??????????? /* Needed in order for the segments to be updated */
> > > > +??????????? arch_kexec_unprotect_crashkres();
> > > > +
> > > > +??????????? /* Differentiate between normal load and hotplug update */
> > > > +??????????? image->hp_action = hp_action;
> > > > +
> > > > +??????????? /* Now invoke arch-specific update handler */
> > > > +??????????? arch_crash_handle_hotplug_event(image);
> > > > +
> > > > +??????????? /* No longer handling a hotplug event */
> > > > +??????????? image->hp_action = KEXEC_CRASH_HP_NONE;
> > > > +??????????? image->elfcorehdr_updated = true;
> > > 
> > > It's good to initialize the image->hp_action here, however where do
> > > you check it? Do you plan to add some check somewhere?
> > 
> > Hi Baoquan,
> > The hp_action member is initialized to 0 in do_image_alloc_init(). I've
> > mapped KEXEC_CRASH_HP_NONE onto 0 on purpose.
> > 
> > But the use of image->hp_action = KEXEC_CRASH_HP_NONE is to actually
> > delineate that a hotplug event handling has completed. You can see
> > imae->hp_action set to hp_action to capture what the triggering event
> > was, as passed into this function.
> > 
> > I will go ahead and set image->hp_action = KEXEC_CRASH_HP_NONE; explicitly
> > in do_kimage_alloc_init(), as that is done for the other crash hotplug members.
> > 
> > Thanks!
> > eric
> 
> Baoquan, as you are currently working through v19, please let me know when I
> should put out v20 with this and Sourabh's feedback.
> Thanks,
> eric

The overall serial looks good to me other than the nitpicks.