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Date: Sun, 23 Jun 2024 18:11:38 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Tianrui Zhao <zhaotianrui@...ngson.cn>, WANG Xuerui <kernel@...0n.name>, kvm@...r.kernel.org,
loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/4] LoongArch: KVM: Add HW Binary Translation
extension support
Hi, Bibo,
On Mon, May 27, 2024 at 3:46 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> Loongson Binary Translation (LBT) is used to accelerate binary translation,
> which contains 4 scratch registers (scr0 to scr3), x86/ARM eflags (eflags)
> and x87 fpu stack pointer (ftop).
>
> Like FPU extension, here late enabling method is used for LBT. LBT context
> is saved/restored on vcpu context switch path.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
> arch/loongarch/include/asm/kvm_host.h | 8 ++++
> arch/loongarch/include/asm/kvm_vcpu.h | 10 +++++
> arch/loongarch/kvm/exit.c | 9 ++++
> arch/loongarch/kvm/vcpu.c | 59 ++++++++++++++++++++++++++-
> 4 files changed, 85 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
> index 2eb2f7572023..88023ab59486 100644
> --- a/arch/loongarch/include/asm/kvm_host.h
> +++ b/arch/loongarch/include/asm/kvm_host.h
> @@ -133,6 +133,7 @@ enum emulation_result {
> #define KVM_LARCH_LASX (0x1 << 2)
> #define KVM_LARCH_SWCSR_LATEST (0x1 << 3)
> #define KVM_LARCH_HWCSR_USABLE (0x1 << 4)
> +#define KVM_LARCH_LBT (0x1 << 5)
>
> struct kvm_vcpu_arch {
> /*
> @@ -166,6 +167,7 @@ struct kvm_vcpu_arch {
>
> /* FPU state */
> struct loongarch_fpu fpu FPU_ALIGN;
> + struct loongarch_lbt lbt;
>
> /* CSR state */
> struct loongarch_csrs *csr;
> @@ -235,6 +237,12 @@ static inline bool kvm_guest_has_lasx(struct kvm_vcpu_arch *arch)
> return arch->cpucfg[2] & CPUCFG2_LASX;
> }
>
> +static inline bool kvm_guest_has_lbt(struct kvm_vcpu_arch *arch)
> +{
> + return arch->cpucfg[2] & (CPUCFG2_X86BT | CPUCFG2_ARMBT
> + | CPUCFG2_MIPSBT);
> +}
> +
> /* Debug: dump vcpu state */
> int kvm_arch_vcpu_dump_regs(struct kvm_vcpu *vcpu);
>
> diff --git a/arch/loongarch/include/asm/kvm_vcpu.h b/arch/loongarch/include/asm/kvm_vcpu.h
> index d7e51300a89f..ec46009be29b 100644
> --- a/arch/loongarch/include/asm/kvm_vcpu.h
> +++ b/arch/loongarch/include/asm/kvm_vcpu.h
> @@ -75,6 +75,16 @@ static inline void kvm_save_lasx(struct loongarch_fpu *fpu) { }
> static inline void kvm_restore_lasx(struct loongarch_fpu *fpu) { }
> #endif
>
> +#ifdef CONFIG_CPU_HAS_LBT
> +int kvm_own_lbt(struct kvm_vcpu *vcpu);
> +#else
> +static inline int kvm_own_lbt(struct kvm_vcpu *vcpu) { return -EINVAL; }
> +static inline void kvm_lose_lbt(struct kvm_vcpu *vcpu) { }
> +static inline void kvm_enable_lbt_fpu(struct kvm_vcpu *vcpu,
> + unsigned long fcsr) { }
> +static inline void kvm_check_fcsr(struct kvm_vcpu *vcpu) { }
> +#endif
It is better to keep symmetry here. That means also declare
kvm_lose_lbt for CONFIG_CPU_HAS_LBT, and move the last two functions
to .c because they are static.
> +
> void kvm_init_timer(struct kvm_vcpu *vcpu, unsigned long hz);
> void kvm_reset_timer(struct kvm_vcpu *vcpu);
> void kvm_save_timer(struct kvm_vcpu *vcpu);
> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
> index e2abd97fb13f..e1bd81d27fd8 100644
> --- a/arch/loongarch/kvm/exit.c
> +++ b/arch/loongarch/kvm/exit.c
> @@ -835,6 +835,14 @@ static int kvm_handle_hypercall(struct kvm_vcpu *vcpu)
> return ret;
> }
>
> +static int kvm_handle_lbt_disabled(struct kvm_vcpu *vcpu)
> +{
> + if (kvm_own_lbt(vcpu))
> + kvm_queue_exception(vcpu, EXCCODE_INE, 0);
> +
> + return RESUME_GUEST;
> +}
> +
> /*
> * LoongArch KVM callback handling for unimplemented guest exiting
> */
> @@ -867,6 +875,7 @@ static exit_handle_fn kvm_fault_tables[EXCCODE_INT_START] = {
> [EXCCODE_LASXDIS] = kvm_handle_lasx_disabled,
> [EXCCODE_GSPR] = kvm_handle_gspr,
> [EXCCODE_HVC] = kvm_handle_hypercall,
> + [EXCCODE_BTDIS] = kvm_handle_lbt_disabled,
> };
>
> int kvm_handle_fault(struct kvm_vcpu *vcpu, int fault)
> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
> index 382796f1d3e6..8f80d1a2dcbb 100644
> --- a/arch/loongarch/kvm/vcpu.c
> +++ b/arch/loongarch/kvm/vcpu.c
> @@ -6,6 +6,7 @@
> #include <linux/kvm_host.h>
> #include <linux/entry-kvm.h>
> #include <asm/fpu.h>
> +#include <asm/lbt.h>
> #include <asm/loongarch.h>
> #include <asm/setup.h>
> #include <asm/time.h>
> @@ -952,12 +953,64 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
> return 0;
> }
>
> +#ifdef CONFIG_CPU_HAS_LBT
> +int kvm_own_lbt(struct kvm_vcpu *vcpu)
> +{
> + if (!kvm_guest_has_lbt(&vcpu->arch))
> + return -EINVAL;
> +
> + preempt_disable();
> + set_csr_euen(CSR_EUEN_LBTEN);
> +
> + _restore_lbt(&vcpu->arch.lbt);
> + vcpu->arch.aux_inuse |= KVM_LARCH_LBT;
> + preempt_enable();
> + return 0;
> +}
> +
> +static void kvm_lose_lbt(struct kvm_vcpu *vcpu)
> +{
> + preempt_disable();
> + if (vcpu->arch.aux_inuse & KVM_LARCH_LBT) {
> + _save_lbt(&vcpu->arch.lbt);
> + clear_csr_euen(CSR_EUEN_LBTEN);
> + vcpu->arch.aux_inuse &= ~KVM_LARCH_LBT;
> + }
> + preempt_enable();
> +}
> +
> +static void kvm_enable_lbt_fpu(struct kvm_vcpu *vcpu, unsigned long fcsr)
It is better to rename it to kvm_own_lbt_tm().
> +{
> + /*
> + * if TM is enabled, top register save/restore will
> + * cause lbt exception, here enable lbt in advance
> + */
> + if (fcsr & FPU_CSR_TM)
> + kvm_own_lbt(vcpu);
> +}
> +
> +static void kvm_check_fcsr(struct kvm_vcpu *vcpu)
> +{
> + unsigned long fcsr;
> +
> + if (vcpu->arch.aux_inuse & KVM_LARCH_FPU)
> + if (!(vcpu->arch.aux_inuse & KVM_LARCH_LBT)) {
The condition can be simplified " if (vcpu->arch.aux_inuse &
(KVM_LARCH_FPU|KVM_LARCH_LBT) == KVM_LARCH_FPU)"
> + fcsr = read_fcsr(LOONGARCH_FCSR0);
> + kvm_enable_lbt_fpu(vcpu, fcsr);
> + }
> +}
> +#endif
> +
> /* Enable FPU and restore context */
> void kvm_own_fpu(struct kvm_vcpu *vcpu)
> {
> preempt_disable();
>
> - /* Enable FPU */
> + /*
> + * Enable FPU for guest
> + * We set FR and FRE according to guest context
> + */
> + kvm_enable_lbt_fpu(vcpu, vcpu->arch.fpu.fcsr);
> set_csr_euen(CSR_EUEN_FPEN);
>
> kvm_restore_fpu(&vcpu->arch.fpu);
> @@ -977,6 +1030,7 @@ int kvm_own_lsx(struct kvm_vcpu *vcpu)
> preempt_disable();
>
> /* Enable LSX for guest */
> + kvm_enable_lbt_fpu(vcpu, vcpu->arch.fpu.fcsr);
> set_csr_euen(CSR_EUEN_LSXEN | CSR_EUEN_FPEN);
> switch (vcpu->arch.aux_inuse & KVM_LARCH_FPU) {
> case KVM_LARCH_FPU:
> @@ -1011,6 +1065,7 @@ int kvm_own_lasx(struct kvm_vcpu *vcpu)
>
> preempt_disable();
>
> + kvm_enable_lbt_fpu(vcpu, vcpu->arch.fpu.fcsr);
> set_csr_euen(CSR_EUEN_FPEN | CSR_EUEN_LSXEN | CSR_EUEN_LASXEN);
> switch (vcpu->arch.aux_inuse & (KVM_LARCH_FPU | KVM_LARCH_LSX)) {
> case KVM_LARCH_LSX:
> @@ -1042,6 +1097,7 @@ void kvm_lose_fpu(struct kvm_vcpu *vcpu)
> {
> preempt_disable();
>
> + kvm_check_fcsr(vcpu);
> if (vcpu->arch.aux_inuse & KVM_LARCH_LASX) {
> kvm_save_lasx(&vcpu->arch.fpu);
> vcpu->arch.aux_inuse &= ~(KVM_LARCH_LSX | KVM_LARCH_FPU | KVM_LARCH_LASX);
> @@ -1064,6 +1120,7 @@ void kvm_lose_fpu(struct kvm_vcpu *vcpu)
> /* Disable FPU */
> clear_csr_euen(CSR_EUEN_FPEN);
> }
> + kvm_lose_lbt(vcpu);
>
> preempt_enable();
> }
> --
> 2.39.3
>
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