linux-kernel - RE: [PATCH 1/3] Drivers: hv: Make portions of Hyper-V init code be arch neutral

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Message-ID: <MWHPR21MB15930361106EDB7183D3505CD7159@MWHPR21MB1593.namprd21.prod.outlook.com>
Date:   Mon, 12 Jul 2021 18:41:21 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Wei Liu <wei.liu@...nel.org>
CC:     Stephen Hemminger <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>, "arnd@...db.de" <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: RE: [PATCH 1/3] Drivers: hv: Make portions of Hyper-V init code be
 arch neutral

From: Wei Liu <wei.liu@...nel.org> Sent: Monday, July 12, 2021 11:24 AM
> 
> On Sun, Jul 11, 2021 at 08:25:14PM -0700, Michael Kelley wrote:
> [...]
> > +int hv_common_cpu_init(unsigned int cpu)
> > +{
> > +	void **inputarg, **outputarg;
> > +	u64 msr_vp_index;
> > +	gfp_t flags;
> > +	int pgcount = hv_root_partition ? 2 : 1;
> > +
> > +	/* hv_cpu_init() can be called with IRQs disabled from hv_resume() */
> > +	flags = irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL;
> > +
> > +	inputarg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg);
> > +	*inputarg = kmalloc(pgcount * HV_HYP_PAGE_SIZE, flags);
> 
> This is changed from alloc_pages to kmalloc. Does it ensure the
> alignment is still correct?
> 
> Wei.

It does.  The alignment guarantee made by kmalloc() was changed a
couple of years ago.  See commit 59bb47985c1d.  Here's the current text
from the comments preceding kmalloc():

* The allocated object address is aligned to at least ARCH_KMALLOC_MINALIGN
 * bytes. For @size of power of two bytes, the alignment is also guaranteed
 * to be at least to the size.

Michael