Re: [PATCH v2 1/2] KVM: arm64: Allow userspace to change ID_AA64PFR1_EL1
From: Shaoqin Huang
Date: Tue Jun 18 2024 - 23:14:29 EST
Hi Marc,
On 6/18/24 15:39, Marc Zyngier wrote:
On Tue, 18 Jun 2024 07:38:06 +0100,
Shaoqin Huang <shahuang@xxxxxxxxxx> wrote:
Allow userspace to change the guest-visible value of the register with
some severe limitation:
- No changes to features not virtualized by KVM (MPAM_frac, RAS_frac)
---
arch/arm64/kvm/sys_regs.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 22b45a15d068..bead81867bce 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2306,7 +2306,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
ID_AA64PFR0_EL1_GIC |
ID_AA64PFR0_EL1_AdvSIMD |
ID_AA64PFR0_EL1_FP), },
- ID_SANITISED(ID_AA64PFR1_EL1),
+ ID_WRITABLE(ID_AA64PFR1_EL1, ~(ID_AA64PFR1_EL1_RAS_frac |
+ ID_AA64PFR1_EL1_MPAM_frac)),
ID_UNALLOCATED(4,2),
ID_UNALLOCATED(4,3),
ID_WRITABLE(ID_AA64ZFR0_EL1, ~ID_AA64ZFR0_EL1_RES0),
This isn't a valid patch.
Furthermore, how about all the other features that may or may not be
currently handled by KVM? Please see [1] and make sure that all
existing fields have a known behaviour (a combination of masked,
preserved, capped, writable or read-only).
I can at least see problems with MTE_frac and MTEX, plus all the other
things that KVM doesn't know how to save/restore (THE, GCS, NMI...).
What I asked you to handle the whole register, I really meant it.
Thanks for pointing out the problem. I will figure those field out and
update this patch later on.
M.
[1] https://developer.arm.com/documentation/ddi0601/2024-03/AArch64-Registers/ID-AA64PFR1-EL1--AArch64-Processor-Feature-Register-1?lang=en
Ok I found that I used the obsolete ARM document so I didn't see the
MTE_frac and MTEX. Thanks for letting me know the latest ARM document.
Thanks,
Shaoqin
--
Shaoqin