linux-kernel - Re: [PATCH 2/3] arm64/kvm: Fine grain _EL2 system registers list that affect nested virtualization

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Message-ID: <87bkdy3z1z.wl-maz@kernel.org>
Date:   Tue, 19 Sep 2023 17:31:04 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Miguel Luis <miguel.luis@...cle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>
Subject: Re: [PATCH 2/3] arm64/kvm: Fine grain _EL2 system registers list that affect nested virtualization

On Tue, 19 Sep 2023 15:54:53 +0100,
Miguel Luis <miguel.luis@...cle.com> wrote:
> 
> Hi Marc,
> 
> > On 18 Sep 2023, at 09:40, Marc Zyngier <maz@...nel.org> wrote:
> > 
> > Hi Miguel,
> > 
> > On Wed, 13 Sep 2023 19:52:07 +0100,
> > Miguel Luis <miguel.luis@...cle.com> wrote:
> >> 
> >> Some _EL1 registers got included in the _EL2 ranges, which are not
> >> affected by NV. Remove them and fine grain the ranges to exclusively
> >> include the _EL2 ones.
> >> 
> >> Signed-off-by: Miguel Luis <miguel.luis@...cle.com>
> >> ---
> >> arch/arm64/kvm/emulate-nested.c | 44 ++++++++++++++++++++++++++++-----
> >> 1 file changed, 38 insertions(+), 6 deletions(-)
> >> 
> >> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> >> index 9ced1bf0c2b7..9aa1c06abdb7 100644
> >> --- a/arch/arm64/kvm/emulate-nested.c
> >> +++ b/arch/arm64/kvm/emulate-nested.c
> >> @@ -649,14 +649,46 @@ static const struct encoding_to_trap_config encoding_to_cgt[] __initconst = {
> >> SR_TRAP(SYS_APGAKEYHI_EL1, CGT_HCR_APK),
> >> /* All _EL2 registers */
> >> SR_RANGE_TRAP(sys_reg(3, 4, 0, 0, 0),
> >> -       sys_reg(3, 4, 3, 15, 7), CGT_HCR_NV),
> >> + sys_reg(3, 4, 4, 0, 1), CGT_HCR_NV),
> > 
> > It would be good if the commit message explained that you are folding
> > SPSR/ELR into the existing range. Also, please keep the two ends of
> > the ranges vertically aligned.
> > 
> 
> OK.
> 
> >> /* Skip the SP_EL1 encoding... */
> >> - SR_TRAP(SYS_SPSR_EL2, CGT_HCR_NV),
> >> - SR_TRAP(SYS_ELR_EL2, CGT_HCR_NV),
> >> - SR_RANGE_TRAP(sys_reg(3, 4, 4, 1, 1),
> >> -       sys_reg(3, 4, 10, 15, 7), CGT_HCR_NV),
> >> + SR_RANGE_TRAP(sys_reg(3, 4, 4, 3, 0),
> >> + sys_reg(3, 4, 10, 6, 7), CGT_HCR_NV),
> >> + /* skip MECID_A0_EL2, MECID_A1_EL2, MECID_P0_EL2,
> >> +  *      MECID_P1_EL2, MECIDR_EL2, VMECID_A_EL2,
> >> +  *      VMECID_P_EL2.
> >> +  */
> > 
> > Please follow the kernel comment format. Also, why are you skipping
> > the MEC registers, but not the MPAM ones? At least indicate a
> > rationale for this.
> > 
> 
> I’m not aware of any exceptions for MPAM registers, although there
> are for MEC when HCR_EL2.NV2 is 0.

Then this rationale should probably be captured here.

> 
> >> SR_RANGE_TRAP(sys_reg(3, 4, 12, 0, 0),
> >> -       sys_reg(3, 4, 14, 15, 7), CGT_HCR_NV),
> >> + sys_reg(3, 4, 12, 1, 1), CGT_HCR_NV),
> >> + /* ICH_AP0R<m>_EL2 */
> >> + SR_RANGE_TRAP(SYS_ICH_AP0R0_EL2,
> >> + SYS_ICH_AP0R3_EL2, CGT_HCR_NV),
> >> + /* ICH_AP1R<m>_EL2 */
> >> + SR_RANGE_TRAP(SYS_ICH_AP1R0_EL2,
> >> + SYS_ICH_AP1R3_EL2, CGT_HCR_NV),
> >> + SR_RANGE_TRAP(sys_reg(3, 4, 12, 9, 5),
> >> + sys_reg(3, 4, 12, 11, 7), CGT_HCR_NV),
> >> + /* ICH_LR<m>_EL2 */
> >> + SR_TRAP(SYS_ICH_LR0_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR1_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR2_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR3_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR4_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR5_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR6_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR7_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR8_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR9_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR10_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR11_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR12_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR13_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR14_EL2, CGT_HCR_NV),
> >> + SR_TRAP(SYS_ICH_LR15_EL2, CGT_HCR_NV),
> > 
> > You could describe all the LRs a single range.
> > 
> 
> Should we skip the gap between LR7 - LR8 ?

Which gap? LRn n described by (3,4,12,12,n) when n is in [0-7], and
(3,4,12,13,n-8) when n is in [8-15]. These two ranges are contiguous.

> 
> >> + SR_RANGE_TRAP(sys_reg(3, 4, 13, 0, 1),
> >> + sys_reg(3, 4, 13, 0, 7), CGT_HCR_NV),
> >> + /* skip AMEVCNTVOFF0<n>_EL2 and AMEVCNTVOFF1<n>_EL2 */
> > 
> > Why?
> 
> I didn’t find its definition TBH although these could use a single range.

D19.6.11 and following?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.