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[Qemu-devel] [Bug 1817846] Re: Qemu 3.1 Aarch64 TLBI VAE1, x0
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [Bug 1817846] Re: Qemu 3.1 Aarch64 TLBI VAE1, x0 |
Date: |
Mon, 04 Mar 2019 15:58:41 -0000 |
Could you provide a test binary (and the QEMU command line to run it)
that demonstrates the bug, please?
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https://bugs.launchpad.net/bugs/1817846
Title:
Qemu 3.1 Aarch64 TLBI VAE1, x0
Status in QEMU:
New
Bug description:
Hello,
In my code I'm trying to remove some permissions to a 4KiB MMU
descriptor. After that I invalidate the MMU with
TLBI VAE1, x0
where x0 is the start of the address of the 4 KiB page.
In Qemu 2.12 this did not work, but I worked around it with:
/* invalidate the address */
TLBI VAE1, x0
/*****************************************************************/
/*****************************************************************/
/* NOTE: THIS IS A TRICK FOR QEMU!!!!!!!!!!!!
*/
/* Apparently we have to change the TTBR0_EL1 when we change a descriptor
(especially to remove permissions) */
/* Otherwise qemu (2.12) will continue with the same descriptor with
permissions! **/
/*****************************************************************/
/*****************************************************************/
/* do a trick (in qemu) */
mrs x1 , TTBR0_EL1
ldr x2 , =kernelTable0Table
msr TTBR0_EL1 , x2
isb
msr TTBR0_EL1 , x1
/* return from function */
ret
That is, I just replaced the TTBR0_EL1 with a temporary value, and then
restored it. (guess qemu 2.12 just needed to reload the values again).
However, even this procedure is not working with qemu 3.1. (I just
tested again with qemu 2.12 and the code works fine, with qemu 3.1 it
does not).
Thanks,
Pharos team
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- [Qemu-devel] [Bug 1817846] Re: Qemu 3.1 Aarch64 TLBI VAE1, x0,
Peter Maydell <=