linux-kernel - Re: [PATCH v8 2/7] kexec: define functions to map and unmap segments

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Message-ID: <c76a6a741b6f465d270153b65ea6f728383ca608.camel@linux.ibm.com>
Date: Thu, 20 Feb 2025 12:22:23 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: steven chen <chenste@...ux.microsoft.com>, stefanb@...ux.ibm.com,
        roberto.sassu@...weicloud.com, roberto.sassu@...wei.com,
        eric.snowberg@...cle.com, ebiederm@...ssion.com, paul@...l-moore.com,
        code@...icks.com, bauermann@...abnow.com,
        linux-integrity@...r.kernel.org, kexec@...ts.infradead.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: madvenka@...ux.microsoft.com, nramas@...ux.microsoft.com,
        James.Bottomley@...senPartnership.com, bhe@...hat.com,
        vgoyal@...hat.com, dyoung@...hat.com
Subject: Re: [PATCH v8 2/7] kexec: define functions to map and unmap segments

Hi Steven,

On Tue, 2025-02-18 at 14:54 -0800, steven chen wrote:
> Currently, the mechanism to map and unmap segments to the kimage
> structure is not available to the subsystems outside of kexec.  This
> functionality is needed when IMA is allocating the memory segments
> during kexec 'load' operation.  Implement functions to map and unmap
> segments to kimage.

Obviously up to now Kexec was mapping the segments. Missing from this patch description is
the reason "why" these functions are needed now.  It's not enough to say "is needed when
IMA is allocating the memory segments during kexec 'load' operation".  The question is why
does "IMA" need to allocate the memory segments.  Don't make the kexec/kexec_dump
maintainers guess.

Refer to the section "Describe your changes" in
https://www.kernel.org/doc/Documentation/process/submitting-patches.rst

> 
> Implement kimage_map_segment() to enable mapping of IMA buffer source
> pages to the kimage structure post kexec 'load'.  This function,
> accepting a kimage pointer, an address, and a size, will gather the
> source pages within the specified address range, create an array of page
> pointers, and map these to a contiguous virtual address range.  The
> function returns the start of this range if successful, or NULL if
> unsuccessful.
> 
> Implement kimage_unmap_segment() for unmapping segments
> using vunmap().
> 
> From: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
> Author: Tushar Sugandhi <tusharsu@...ux.microsoft.com>

Again, no such thing as an "Author" tag.  Refer to the comments on 1/7.

> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>

As previously requested, please add the Cc's inline here and in all the kexec/kdump
related patches:

Cc: Eric Biederman <ebiederm@...ssion.com>
Cc: Baoquan He <bhe@...hat.com> 
Cc: Vivek Goyal <vgoyal@...hat.com>
Cc: Dave Young <dyoung@...hat.com>

> Signed-off-by: steven chen <chenste@...ux.microsoft.com>

thanks,

Mimi