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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Dave Young <dyoung@redhat.com>
Cc: linux-efi <linux-efi@vger.kernel.org>,
	Kexec Mailing List <kexec@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Matthew Garrett <matthewgarrett@google.com>,
	Bhupesh Sharma <bhsharma@redhat.com>
Subject: Re: [PATCH] do not clean dummy variable in kexec path
Date: Mon, 5 Aug 2019 18:55:03 +0300	[thread overview]
Message-ID: <CAKv+Gu-my6EpLfxBnbMn21be62oHrF6PKFu2rt-4Pqk9wG9SXA@mail.gmail.com> (raw)
In-Reply-To: <20190805083553.GA27708@dhcp-128-65.nay.redhat.com>

On Mon, 5 Aug 2019 at 11:36, Dave Young <dyoung@redhat.com> wrote:
>
> kexec reboot fails randomly in UEFI based kvm guest.  The firmware
> just reset while calling efi_delete_dummy_variable();  Unfortunately
> I don't know how to debug the firmware, it is also possible a potential
> problem on real hardware as well although nobody reproduced it.
>
> The intention of efi_delete_dummy_variable is to trigger garbage collection
> when entering virtual mode.  But SetVirtualAddressMap can only run once
> for each physical reboot, thus kexec_enter_virtual_mode is not necessarily
> a good place to clean dummy object.
>

I would argue that this means it is not a good place to *create* the
dummy variable, and if we don't create it, we don't have to delete it
either.

> Drop efi_delete_dummy_variable so that kexec reboot can work.
>

Creating it and not deleting it is bad, so please try and see if we
can omit the creation on this code path instead.


> Signed-off-by: Dave Young <dyoung@redhat.com>
> ---
>  arch/x86/platform/efi/efi.c |    3 ---
>  1 file changed, 3 deletions(-)
>
> --- linux-x86.orig/arch/x86/platform/efi/efi.c
> +++ linux-x86/arch/x86/platform/efi/efi.c
> @@ -894,9 +894,6 @@ static void __init kexec_enter_virtual_m
>
>         if (efi_enabled(EFI_OLD_MEMMAP) && (__supported_pte_mask & _PAGE_NX))
>                 runtime_code_page_mkexec();
> -
> -       /* clean DUMMY object */
> -       efi_delete_dummy_variable();
>  #endif
>  }
>

  reply	other threads:[~2019-08-05 15:55 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-05  8:35 Dave Young
2019-08-05 15:55 ` Ard Biesheuvel [this message]
2019-08-06  2:41   ` Dave Young
2019-08-08  7:49   ` Dave Young
2019-08-05 17:09 ` Matthew Garrett
2019-08-06  2:44   ` Dave Young

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