Subject: Re: [PATCH v8 07/11] KVM: arm64: Add handlers for protected VM System Registers

From: Marc Zyngier <[email-masked]>
Date: Mon, 11 Oct 2021 12:39:44 +0100

On Sun, 10 Oct 2021 15:56:32 +0100,
Fuad Tabba <[email-masked]> wrote:
> 
> Add system register handlers for protected VMs. These cover Sys64
> registers (including feature id registers), and debug.
> 
> No functional change intended as these are not hooked in yet to
> the guest exit handlers introduced earlier. So when trapping is
> triggered, the exit handlers let the host handle it, as before.
> 
> Reviewed-by: Andrew Jones <[email-masked]>
> Signed-off-by: Fuad Tabba <[email-masked]>

[...]

> +/*
> + * Architected system registers.
> + * Important: Must be sorted ascending by Op0, Op1, CRn, CRm, Op2
> + *
> + * NOTE: Anything not explicitly listed here is *restricted by default*, i.e.,
> + * it will lead to injecting an exception into the guest.
> + */
> +static const struct sys_reg_desc pvm_sys_reg_descs[] = {
> +	/* Cache maintenance by set/way operations are restricted. */
> +
> +	/* Debug and Trace Registers are restricted. */
> +
> +	/* AArch64 mappings of the AArch32 ID registers */
> +	/* CRm=1 */
> +	AARCH32(SYS_ID_PFR0_EL1),
> +	AARCH32(SYS_ID_PFR1_EL1),
> +	AARCH32(SYS_ID_DFR0_EL1),
> +	AARCH32(SYS_ID_AFR0_EL1),
> +	AARCH32(SYS_ID_MMFR0_EL1),
> +	AARCH32(SYS_ID_MMFR1_EL1),
> +	AARCH32(SYS_ID_MMFR2_EL1),
> +	AARCH32(SYS_ID_MMFR3_EL1),
> +
> +	/* CRm=2 */
> +	AARCH32(SYS_ID_ISAR0_EL1),
> +	AARCH32(SYS_ID_ISAR1_EL1),
> +	AARCH32(SYS_ID_ISAR2_EL1),
> +	AARCH32(SYS_ID_ISAR3_EL1),
> +	AARCH32(SYS_ID_ISAR4_EL1),
> +	AARCH32(SYS_ID_ISAR5_EL1),
> +	AARCH32(SYS_ID_MMFR4_EL1),
> +	AARCH32(SYS_ID_ISAR6_EL1),
> +
> +	/* CRm=3 */
> +	AARCH32(SYS_MVFR0_EL1),
> +	AARCH32(SYS_MVFR1_EL1),
> +	AARCH32(SYS_MVFR2_EL1),
> +	AARCH32(SYS_ID_PFR2_EL1),
> +	AARCH32(SYS_ID_DFR1_EL1),
> +	AARCH32(SYS_ID_MMFR5_EL1),
> +
> +	/* AArch64 ID registers */
> +	/* CRm=4 */
> +	AARCH64(SYS_ID_AA64PFR0_EL1),
> +	AARCH64(SYS_ID_AA64PFR1_EL1),
> +	AARCH64(SYS_ID_AA64ZFR0_EL1),
> +	AARCH64(SYS_ID_AA64DFR0_EL1),
> +	AARCH64(SYS_ID_AA64DFR1_EL1),
> +	AARCH64(SYS_ID_AA64AFR0_EL1),
> +	AARCH64(SYS_ID_AA64AFR1_EL1),
> +	AARCH64(SYS_ID_AA64ISAR0_EL1),
> +	AARCH64(SYS_ID_AA64ISAR1_EL1),
> +	AARCH64(SYS_ID_AA64MMFR0_EL1),
> +	AARCH64(SYS_ID_AA64MMFR1_EL1),
> +	AARCH64(SYS_ID_AA64MMFR2_EL1),
> +
> +	HOST_HANDLED(SYS_SCTLR_EL1),
> +	HOST_HANDLED(SYS_ACTLR_EL1),
> +	HOST_HANDLED(SYS_CPACR_EL1),
> +
> +	HOST_HANDLED(SYS_RGSR_EL1),
> +	HOST_HANDLED(SYS_GCR_EL1),

What is the expected semantics of this handling? These registers are
free to use by the guest unless MTE is disabled. Either the guest
accesses them directly (no trap), accesses them while MTE is disabled
(trap), or access them when MTE doesn't exist.

The first and last cases are invisible to EL2. For the second case,
why should we go back to EL1 rather than injecting an UNDEF directly?

> +
> +	/* Scalable Vector Registers are restricted. */
> +
> +	HOST_HANDLED(SYS_TTBR0_EL1),
> +	HOST_HANDLED(SYS_TTBR1_EL1),
> +	HOST_HANDLED(SYS_TCR_EL1),

None of these should normally trap unless we are handling an erratum
(such as Cavium 219) or that we have HCR_EL2.TVM set. The former is
handled at EL2, and I don't expect any Set/Way emulation to require
the latter.

> +
> +	HOST_HANDLED(SYS_APIAKEYLO_EL1),
> +	HOST_HANDLED(SYS_APIAKEYHI_EL1),
> +	HOST_HANDLED(SYS_APIBKEYLO_EL1),
> +	HOST_HANDLED(SYS_APIBKEYHI_EL1),
> +	HOST_HANDLED(SYS_APDAKEYLO_EL1),
> +	HOST_HANDLED(SYS_APDAKEYHI_EL1),
> +	HOST_HANDLED(SYS_APDBKEYLO_EL1),
> +	HOST_HANDLED(SYS_APDBKEYHI_EL1),
> +	HOST_HANDLED(SYS_APGAKEYLO_EL1),
> +	HOST_HANDLED(SYS_APGAKEYHI_EL1),

This is debatable too. If the guest has started using PtrAuth and that
we haven't handled things in fixup_guest_exit(), why returning to the
host? This should directly UNDEF.

> +
> +	HOST_HANDLED(SYS_AFSR0_EL1),
> +	HOST_HANDLED(SYS_AFSR1_EL1),
> +	HOST_HANDLED(SYS_ESR_EL1),

Same as TTBR*/TCR.

> +
> +	HOST_HANDLED(SYS_ERRIDR_EL1),
> +	HOST_HANDLED(SYS_ERRSELR_EL1),
> +	HOST_HANDLED(SYS_ERXFR_EL1),
> +	HOST_HANDLED(SYS_ERXCTLR_EL1),
> +	HOST_HANDLED(SYS_ERXSTATUS_EL1),
> +	HOST_HANDLED(SYS_ERXADDR_EL1),
> +	HOST_HANDLED(SYS_ERXMISC0_EL1),
> +	HOST_HANDLED(SYS_ERXMISC1_EL1),

This really should be handled as RAZ/WI at EL2.

> +
> +	HOST_HANDLED(SYS_TFSR_EL1),
> +	HOST_HANDLED(SYS_TFSRE0_EL1),

Same as RCSR/GSR.

> +
> +	HOST_HANDLED(SYS_FAR_EL1),

Same as TTBR

> +	HOST_HANDLED(SYS_PAR_EL1),

Does not trap in the absence of FGT (which we don't use yet).

> +
> +	/* Performance Monitoring Registers are restricted. */
> +
> +	HOST_HANDLED(SYS_MAIR_EL1),
> +	HOST_HANDLED(SYS_AMAIR_EL1),

Same as TTBR.

> +
> +	/* Limited Ordering Regions Registers are restricted. */
> +
> +	HOST_HANDLED(SYS_VBAR_EL1),

Doesn't trap in the absence of FGT.

> +	HOST_HANDLED(SYS_DISR_EL1),

If RAS exists, a DISR_EL1 access is routed to VDISR_EL2. If RAS isn't
present, this UNDEFs. In any case, there is no trap.

> +
> +	/* GIC CPU Interface registers are restricted. */

Err... Does this include ICC_SGI*R_EL1/ICC_SRE_EL1? Not going to work
if you don't let EL1 dealing with this.

> +
> +	HOST_HANDLED(SYS_CONTEXTIDR_EL1),

Same as TTBR.

> +	HOST_HANDLED(SYS_TPIDR_EL1),

Doesn't trap in the absence of FGT.

> +
> +	HOST_HANDLED(SYS_SCXTNUM_EL1),

Should UNDEF at EL2 until we actually enable FEAT_CSV2_2.

> +
> +	HOST_HANDLED(SYS_CNTKCTL_EL1),

Never traps.

> +
> +	HOST_HANDLED(SYS_CCSIDR_EL1),
> +	HOST_HANDLED(SYS_CLIDR_EL1),
> +	HOST_HANDLED(SYS_CSSELR_EL1),
> +	HOST_HANDLED(SYS_CTR_EL0),

Eventually, we should expose a synthetic version of these at EL2.

> +
> +	/* Performance Monitoring Registers are restricted. */
> +
> +	HOST_HANDLED(SYS_TPIDR_EL0),
> +	HOST_HANDLED(SYS_TPIDRRO_EL0),

Do not trap in the absence of FGT.

> +
> +	HOST_HANDLED(SYS_SCXTNUM_EL0),

Should UNDEF at EL2 until we actually enable FEAT_CSV2_2.

> +
> +	/* Activity Monitoring Registers are restricted. */
> +
> +	HOST_HANDLED(SYS_CNTP_TVAL_EL0),
> +	HOST_HANDLED(SYS_CNTP_CTL_EL0),
> +	HOST_HANDLED(SYS_CNTP_CVAL_EL0),
> +
> +	/* Performance Monitoring Registers are restricted. */
> +
> +	HOST_HANDLED(SYS_DACR32_EL2),
> +	HOST_HANDLED(SYS_IFSR32_EL2),
> +	HOST_HANDLED(SYS_FPEXC32_EL2),

I don't understand the presence of these registers here. As the name
indicates, they are 32bit only.

We need a complete overhaul of this table. I'm going to go through the
rest of the patches, and we can then fix this.

Thanks,

	M.

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

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