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[31.30.173.16]) by smtp.gmail.com with ESMTPSA id i3-20020a5d6303000000b0032db4e660d9sm3831000wru.56.2023.10.19.00.57.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Oct 2023 00:57:56 -0700 (PDT) Date: Thu, 19 Oct 2023 09:57:55 +0200 From: Andrew Jones To: Anup Patel Subject: Re: [PATCH v2 3/8] RISC-V: KVM: Allow some SBI extensions to be disabled by default Message-ID: <20231019-1e6f411e1cbc4a3b0fbff3f5@orel> References: <20231012051509.738750-1-apatel@ventanamicro.com> <20231012051509.738750-4-apatel@ventanamicro.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231012051509.738750-4-apatel@ventanamicro.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-serial@vger.kernel.org, kvm@vger.kernel.org, Greg Kroah-Hartman , Atish Patra , linuxppc-dev@lists.ozlabs.org, Conor Dooley , linux-kernel@vger.kernel.org, Palmer Dabbelt , kvm-riscv@lists.infradead.org, Paul Walmsley , Paolo Bonzini , linux-riscv@lists.infradead.org, Jiri Slaby Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Oct 12, 2023 at 10:45:04AM +0530, Anup Patel wrote: > Currently, all SBI extensions are enabled by default which is > problematic for SBI extensions (such as DBCN) which are forwarded > to the KVM user-space because we might have an older KVM user-space > which is not aware/ready to handle newer SBI extensions. Ideally, > the SBI extensions forwarded to the KVM user-space must be > disabled by default. > > To address above, we allow certain SBI extensions to be disabled > by default so that KVM user-space must explicitly enable such > SBI extensions to receive forwarded calls from Guest VCPU. > > Signed-off-by: Anup Patel > --- > arch/riscv/include/asm/kvm_vcpu_sbi.h | 4 +++ > arch/riscv/kvm/vcpu.c | 6 ++++ > arch/riscv/kvm/vcpu_sbi.c | 45 ++++++++++++++++----------- > 3 files changed, 36 insertions(+), 19 deletions(-) > > diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h > index 8d6d4dce8a5e..c02bda5559d7 100644 > --- a/arch/riscv/include/asm/kvm_vcpu_sbi.h > +++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h > @@ -35,6 +35,9 @@ struct kvm_vcpu_sbi_return { > struct kvm_vcpu_sbi_extension { > unsigned long extid_start; > unsigned long extid_end; > + > + bool default_unavail; > + > /** > * SBI extension handler. It can be defined for a given extension or group of > * extension. But it should always return linux error codes rather than SBI > @@ -59,6 +62,7 @@ int kvm_riscv_vcpu_get_reg_sbi_ext(struct kvm_vcpu *vcpu, > const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext( > struct kvm_vcpu *vcpu, unsigned long extid); > int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run); > +void kvm_riscv_vcpu_sbi_init(struct kvm_vcpu *vcpu); > > #ifdef CONFIG_RISCV_SBI_V01 > extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_v01; > diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c > index c061a1c5fe98..e087c809073c 100644 > --- a/arch/riscv/kvm/vcpu.c > +++ b/arch/riscv/kvm/vcpu.c > @@ -141,6 +141,12 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu) > if (rc) > return rc; > > + /* > + * Setup SBI extensions > + * NOTE: This must be the last thing to be initialized. > + */ > + kvm_riscv_vcpu_sbi_init(vcpu); With this, we no longer defer probing to the first access (whether that's by the guest or KVM userspace). With our current small set of SBI extensions where only a single one has a probe function, then this simpler approach is good enough. We can always go back to the lazy approach later if needed. > + > /* Reset VCPU */ > kvm_riscv_reset_vcpu(vcpu); > > diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c > index 9cd97091c723..1b1cee86efda 100644 > --- a/arch/riscv/kvm/vcpu_sbi.c > +++ b/arch/riscv/kvm/vcpu_sbi.c > @@ -155,14 +155,8 @@ static int riscv_vcpu_set_sbi_ext_single(struct kvm_vcpu *vcpu, > if (!sext) > return -ENOENT; > > - /* > - * We can't set the extension status to available here, since it may > - * have a probe() function which needs to confirm availability first, > - * but it may be too early to call that here. We can set the status to > - * unavailable, though. > - */ > - if (!reg_val) > - scontext->ext_status[sext->ext_idx] = > + scontext->ext_status[sext->ext_idx] = (reg_val) ? > + KVM_RISCV_SBI_EXT_AVAILABLE : > KVM_RISCV_SBI_EXT_UNAVAILABLE; We're missing the change to riscv_vcpu_get_sbi_ext_single() which should also drop the comment block explaining the limits to status knowledge without initial probing (which we now do) and then just check for available, i.e. diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c index bb76c3cf633f..92c42d9aba1c 100644 --- a/arch/riscv/kvm/vcpu_sbi.c +++ b/arch/riscv/kvm/vcpu_sbi.c @@ -186,15 +186,8 @@ static int riscv_vcpu_get_sbi_ext_single(struct kvm_vcpu *vcpu, if (!sext) return -ENOENT; - /* - * If the extension status is still uninitialized, then we should probe - * to determine if it's available, but it may be too early to do that - * here. The best we can do is report that the extension has not been - * disabled, i.e. we return 1 when the extension is available and also - * when it only may be available. - */ - *reg_val = scontext->ext_status[sext->ext_idx] != - KVM_RISCV_SBI_EXT_UNAVAILABLE; + *reg_val = scontext->ext_status[sext->ext_idx] == + KVM_RISCV_SBI_EXT_AVAILABLE; return 0; } > > return 0; > @@ -337,18 +331,8 @@ const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext( > scontext->ext_status[entry->ext_idx] == > KVM_RISCV_SBI_EXT_AVAILABLE) > return ext; > - if (scontext->ext_status[entry->ext_idx] == > - KVM_RISCV_SBI_EXT_UNAVAILABLE) > - return NULL; > - if (ext->probe && !ext->probe(vcpu)) { > - scontext->ext_status[entry->ext_idx] = > - KVM_RISCV_SBI_EXT_UNAVAILABLE; > - return NULL; > - } > > - scontext->ext_status[entry->ext_idx] = > - KVM_RISCV_SBI_EXT_AVAILABLE; > - return ext; > + return NULL; > } > } > > @@ -419,3 +403,26 @@ int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run) > > return ret; > } > + > +void kvm_riscv_vcpu_sbi_init(struct kvm_vcpu *vcpu) > +{ > + struct kvm_vcpu_sbi_context *scontext = &vcpu->arch.sbi_context; > + const struct kvm_riscv_sbi_extension_entry *entry; > + const struct kvm_vcpu_sbi_extension *ext; > + int i; > + > + for (i = 0; i < ARRAY_SIZE(sbi_ext); i++) { > + entry = &sbi_ext[i]; > + ext = entry->ext_ptr; > + > + if (ext->probe && !ext->probe(vcpu)) { > + scontext->ext_status[entry->ext_idx] = > + KVM_RISCV_SBI_EXT_UNAVAILABLE; > + continue; > + } > + > + scontext->ext_status[entry->ext_idx] = ext->default_unavail ? > + KVM_RISCV_SBI_EXT_UNAVAILABLE : > + KVM_RISCV_SBI_EXT_AVAILABLE; > + } > +} > -- > 2.34.1 > Thanks, drew