linux-kernel - Re: [PATCHv10.1 09/18] x86/mm: Adding callbacks to prepare encrypted memory for kexec

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Date: Mon, 6 May 2024 16:21:20 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: adrian.hunter@...el.com, ashish.kalra@....com, bhe@...hat.com,
	dave.hansen@...ux.intel.com, elena.reshetova@...el.com,
	jun.nakajima@...el.com, kai.huang@...el.com,
	kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org, ltao@...hat.com, mingo@...hat.com,
	nik.borisov@...e.com, peterz@...radead.org, rafael@...nel.org,
	rick.p.edgecombe@...el.com,
	sathyanarayanan.kuppuswamy@...ux.intel.com, seanjc@...gle.com,
	tglx@...utronix.de, thomas.lendacky@....com, x86@...nel.org
Subject: Re: [PATCHv10.1 09/18] x86/mm: Adding callbacks to prepare encrypted
 memory for kexec

On Mon, May 06, 2024 at 04:22:02PM +0300, Kirill A. Shutemov wrote:
> I do. See comment just above enc_kexec_stop_conversion() call.

If you mean this:

        /*
         * Call enc_kexec_stop_conversion() while all CPUs are still active and
         * interrupts are enabled. This will allow all in-flight memory
         * conversions to finish cleanly.
         */
        if (kexec_in_progress)
                x86_platform.guest.enc_kexec_stop_conversion(false);

then no, this is not enough.

I mean this:

/**
 * struct x86_guest - Functions used by misc guest incarnations like SEV, TDX, etc.
 *
 * @enc_status_change_prepare   Notify HV before the encryption status of a range is changed
 * @enc_status_change_finish    Notify HV after the encryption status of a range is changed
 * @enc_tlb_flush_required      Returns true if a TLB flush is needed before changing page encryption status
 * @enc_cache_flush_required    Returns true if a cache flush is needed before changing page encryption status
 * @enc_kexec_begin		Begin the two-step process of stopping
 * 				page conversion... <insert reason why it
 * 				needs to happen this way, blabla>
 * @enc_kexec_finish		...
 */
struct x86_guest {
        int (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
        int (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
        bool (*enc_tlb_flush_required)(bool enc);
        bool (*enc_cache_flush_required)(void);
        void (*enc_kexec_begin)(bool crash);
        void (*enc_kexec_finish)(void);

And calling them a _begin and _finish makes a lot more sense to me:
_begin starts the kexec process for encrypted guests and _finish
finishes it.

Just from the names you now know what needs to happen and in which
order.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette