Subject: [PATCH v4 28/40] KVM: arm64: Defer saving/restoring 64-bit sysregs to vcpu load/put on VHE

From: [email-masked] (Christoffer Dall)
Date: Thu, 22 Feb 2018 20:48:31 +0100

On Thu, Feb 22, 2018 at 06:30:11PM +0000, Julien Grall wrote:
> Hi Christoffer,
> 
> On 15/02/18 21:03, Christoffer Dall wrote:
> >Some system registers do not affect the host kernel's execution and can
> >therefore be loaded when we are about to run a VCPU and we don't have to
> >restore the host state to the hardware before the time when we are
> >actually about to return to userspace or schedule out the VCPU thread.
> >
> >The EL1 system registers and the userspace state registers only
> >affecting EL0 execution do not need to be saved and restored on every
> >switch between the VM and the host, because they don't affect the host
> >kernel's execution.
> >
> >We mark all registers which are now deffered as such in the
> 
> NIT: s/deffered/deferred/ I think.
> 
> >vcpu_{read,write}_sys_reg accessors in sys-regs.c to ensure the most
> >up-to-date copy is always accessed.
> >
> >Note MPIDR_EL1 (controlled via VMPIDR_EL2) is accessed from other vcpu
> >threads, for example via the GIC emulation, and therefore must be
> >declared as immediate, which is fine as the guest cannot modify this
> >value.
> >
> >The 32-bit sysregs can also be deferred but we do this in a separate
> >patch as it requires a bit more infrastructure.
> 
> 
> [...]
> 
> >diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> >index b3c3f014aa61..f060309337aa 100644
> >--- a/arch/arm64/kvm/sys_regs.c
> >+++ b/arch/arm64/kvm/sys_regs.c
> >@@ -87,6 +87,26 @@ u64 vcpu_read_sys_reg(struct kvm_vcpu *vcpu, int reg)
> >  	 * exit from the guest but are only saved on vcpu_put.
> >  	 */
> >  	switch (reg) {
> >+	case CSSELR_EL1:	return read_sysreg_s(SYS_CSSELR_EL1);
> >+	case SCTLR_EL1:		return read_sysreg_s(sctlr_EL12);
> >+	case ACTLR_EL1:		return read_sysreg_s(SYS_ACTLR_EL1);
> >+	case CPACR_EL1:		return read_sysreg_s(cpacr_EL12);
> >+	case TTBR0_EL1:		return read_sysreg_s(ttbr0_EL12);
> >+	case TTBR1_EL1:		return read_sysreg_s(ttbr1_EL12);
> >+	case TCR_EL1:		return read_sysreg_s(tcr_EL12);
> >+	case ESR_EL1:		return read_sysreg_s(esr_EL12);
> >+	case AFSR0_EL1:		return read_sysreg_s(afsr0_EL12);
> >+	case AFSR1_EL1:		return read_sysreg_s(afsr1_EL12);
> >+	case FAR_EL1:		return read_sysreg_s(far_EL12);
> >+	case MAIR_EL1:		return read_sysreg_s(mair_EL12);
> >+	case VBAR_EL1:		return read_sysreg_s(vbar_EL12);
> >+	case CONTEXTIDR_EL1:	return read_sysreg_s(contextidr_EL12);
> >+	case TPIDR_EL0:		return read_sysreg_s(SYS_TPIDR_EL0);
> >+	case TPIDRRO_EL0:	return read_sysreg_s(SYS_TPIDRRO_EL0);
> 
> I find a bit confusing to have some EL0 registers in the middle of EL1 ones.
> Is it because they are listed by encoding?
> 

They are sorted in the same way as the sysreg array defines.  I can add
that to the commentary.

> >+	case TPIDR_EL1:		return read_sysreg_s(SYS_TPIDR_EL1);
> >+	case AMAIR_EL1:		return read_sysreg_s(amair_EL12);
> >+	case CNTKCTL_EL1:	return read_sysreg_s(cntkctl_EL12);
> >+	case PAR_EL1:		return read_sysreg_s(SYS_PAR_EL1);
> >  	}
> >  immediate_read:
> >@@ -103,6 +123,26 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, int reg, u64 val)
> >  	 * entry to the guest but are only restored on vcpu_load.
> >  	 */
> >  	switch (reg) {
> >+	case CSSELR_EL1:	write_sysreg_s(val, SYS_CSSELR_EL1);	return;
> >+	case SCTLR_EL1:		write_sysreg_s(val, sctlr_EL12);	return;
> >+	case ACTLR_EL1:		write_sysreg_s(val, SYS_ACTLR_EL1);	return;
> >+	case CPACR_EL1:		write_sysreg_s(val, cpacr_EL12);	return;
> >+	case TTBR0_EL1:		write_sysreg_s(val, ttbr0_EL12);	return;
> >+	case TTBR1_EL1:		write_sysreg_s(val, ttbr1_EL12);	return;
> >+	case TCR_EL1:		write_sysreg_s(val, tcr_EL12);		return;
> >+	case ESR_EL1:		write_sysreg_s(val, esr_EL12);		return;
> >+	case AFSR0_EL1:		write_sysreg_s(val, afsr0_EL12);	return;
> >+	case AFSR1_EL1:		write_sysreg_s(val, afsr1_EL12);	return;
> >+	case FAR_EL1:		write_sysreg_s(val, far_EL12);		return;
> >+	case MAIR_EL1:		write_sysreg_s(val, mair_EL12);		return;
> >+	case VBAR_EL1:		write_sysreg_s(val, vbar_EL12);		return;
> >+	case CONTEXTIDR_EL1:	write_sysreg_s(val, contextidr_EL12);	return;
> >+	case TPIDR_EL0:		write_sysreg_s(val, SYS_TPIDR_EL0);	return;
> >+	case TPIDRRO_EL0:	write_sysreg_s(val, SYS_TPIDRRO_EL0);	return;
> >+	case TPIDR_EL1:		write_sysreg_s(val, SYS_TPIDR_EL1);	return;
> >+	case AMAIR_EL1:		write_sysreg_s(val, amair_EL12);	return;
> >+	case CNTKCTL_EL1:	write_sysreg_s(val, cntkctl_EL12);	return;
> >+	case PAR_EL1:		write_sysreg_s(val, SYS_PAR_EL1);	return;
> >  	}
> >  immediate_write:
> >
> 

Thanks,
-Christoffer