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[34.83.12.150]) by smtp.gmail.com with ESMTPSA id f22sm2932671pgk.21.2021.11.03.20.47.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Nov 2021 20:47:46 -0700 (PDT) Date: Wed, 3 Nov 2021 20:47:42 -0700 From: Ricardo Koller To: Reiji Watanabe Cc: Oliver Upton , kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Marc Zyngier , James Morse , Alexandru Elisei , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, Andrew Jones , Peter Shier Subject: Re: [PATCH v2 3/6] KVM: arm64: Allow guest to set the OSLK bit Message-ID: References: <20211102094651.2071532-1-oupton@google.com> <20211102094651.2071532-4-oupton@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Nov 03, 2021 at 08:31:35PM -0700, Reiji Watanabe wrote: > On Tue, Nov 2, 2021 at 2:47 AM Oliver Upton wrote: > > > > Allow writes to OSLAR and forward the OSLK bit to OSLSR. Change the > > reset value of the OSLK bit to 1. Allow the value to be migrated by > > making OSLSR_EL1.OSLK writable from userspace. > > > > Signed-off-by: Oliver Upton > > --- > > arch/arm64/include/asm/sysreg.h | 6 ++++++ > > arch/arm64/kvm/sys_regs.c | 35 +++++++++++++++++++++++++-------- > > 2 files changed, 33 insertions(+), 8 deletions(-) > > > > diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h > > index b268082d67ed..6ba4dc97b69d 100644 > > --- a/arch/arm64/include/asm/sysreg.h > > +++ b/arch/arm64/include/asm/sysreg.h > > @@ -127,7 +127,13 @@ > > #define SYS_DBGWCRn_EL1(n) sys_reg(2, 0, 0, n, 7) > > #define SYS_MDRAR_EL1 sys_reg(2, 0, 1, 0, 0) > > #define SYS_OSLAR_EL1 sys_reg(2, 0, 1, 0, 4) > > + > > +#define SYS_OSLAR_OSLK BIT(0) > > + > > #define SYS_OSLSR_EL1 sys_reg(2, 0, 1, 1, 4) > > + > > +#define SYS_OSLSR_OSLK BIT(1) > > + > > #define SYS_OSDLR_EL1 sys_reg(2, 0, 1, 3, 4) > > #define SYS_DBGPRCR_EL1 sys_reg(2, 0, 1, 4, 4) > > #define SYS_DBGCLAIMSET_EL1 sys_reg(2, 0, 7, 8, 6) > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > > index 0326b3df0736..acd8aa2e5a44 100644 > > --- a/arch/arm64/kvm/sys_regs.c > > +++ b/arch/arm64/kvm/sys_regs.c > > @@ -44,6 +44,10 @@ > > * 64bit interface. > > */ > > > > +static int reg_from_user(u64 *val, const void __user *uaddr, u64 id); > > +static int reg_to_user(void __user *uaddr, const u64 *val, u64 id); > > +static u64 sys_reg_to_index(const struct sys_reg_desc *reg); > > + > > static bool read_from_write_only(struct kvm_vcpu *vcpu, > > struct sys_reg_params *params, > > const struct sys_reg_desc *r) > > @@ -287,6 +291,24 @@ static bool trap_loregion(struct kvm_vcpu *vcpu, > > return trap_raz_wi(vcpu, p, r); > > } > > > > +static bool trap_oslar_el1(struct kvm_vcpu *vcpu, > > + struct sys_reg_params *p, > > + const struct sys_reg_desc *r) > > +{ > > + u64 oslsr; > > + > > + if (!p->is_write) > > + return read_from_write_only(vcpu, p, r); > > + > > + /* Forward the OSLK bit to OSLSR */ > > + oslsr = __vcpu_sys_reg(vcpu, OSLSR_EL1) & ~SYS_OSLSR_OSLK; > > + if (p->regval & SYS_OSLAR_OSLK) > > + oslsr |= SYS_OSLSR_OSLK; > > + > > + __vcpu_sys_reg(vcpu, OSLSR_EL1) = oslsr; > > + return true; > > +} > > + > > static bool trap_oslsr_el1(struct kvm_vcpu *vcpu, > > struct sys_reg_params *p, > > const struct sys_reg_desc *r) > > @@ -309,9 +331,10 @@ static int set_oslsr_el1(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > if (err) > > return err; > > > > - if (val != rd->val) > > + if ((val | SYS_OSLSR_OSLK) != rd->val) > > return -EINVAL; > > > > + __vcpu_sys_reg(vcpu, rd->reg) = val; > > return 0; > > } > > > > @@ -1176,10 +1199,6 @@ static bool access_raz_id_reg(struct kvm_vcpu *vcpu, > > return __access_id_reg(vcpu, p, r, true); > > } > > > > -static int reg_from_user(u64 *val, const void __user *uaddr, u64 id); > > -static int reg_to_user(void __user *uaddr, const u64 *val, u64 id); > > -static u64 sys_reg_to_index(const struct sys_reg_desc *reg); > > - > > /* Visibility overrides for SVE-specific control registers */ > > static unsigned int sve_visibility(const struct kvm_vcpu *vcpu, > > const struct sys_reg_desc *rd) > > @@ -1456,8 +1475,8 @@ static const struct sys_reg_desc sys_reg_descs[] = { > > DBG_BCR_BVR_WCR_WVR_EL1(15), > > > > { SYS_DESC(SYS_MDRAR_EL1), trap_raz_wi }, > > - { SYS_DESC(SYS_OSLAR_EL1), trap_raz_wi }, > > - { SYS_DESC(SYS_OSLSR_EL1), trap_oslsr_el1, reset_val, OSLSR_EL1, 0x00000008, > > + { SYS_DESC(SYS_OSLAR_EL1), trap_oslar_el1 }, > > + { SYS_DESC(SYS_OSLSR_EL1), trap_oslsr_el1, reset_val, OSLSR_EL1, 0x0000000A, > > .set_user = set_oslsr_el1, }, > > Reviewed-by: Reiji Watanabe > > I assume the reason why you changed the reset value for the > register is because Arm ARM says "the On a Cold reset, > this field resets to 1". > > "4.82 KVM_ARM_VCPU_INIT" in Documentation/virt/kvm/api.rst says: > ------------------------------------------------------------- > - System registers: Reset to their architecturally defined > values as for a warm reset to EL1 (resp. SVC) > ------------------------------------------------------------- > > Since Arm ARM doesn't say anything about a warm reset for the field, > I would guess the bit doesn't necessarily need to be set. That would be great, because it would avoid the migration issue that Oliver described in [PATCH v2 4/6]: There is an issue, though, with migration: older KVM will not show OSLSR_EL1 on KVM_GET_REG_LIST. However, in order to provide an architectural OS Lock, its reset value must be 1 (enabled). This would all have the effect of discarding the guest's OS lock value and blocking all debug exceptions intended for the guest until the next reboot. > > Thanks, > Reiji > > > > { SYS_DESC(SYS_OSDLR_EL1), trap_raz_wi }, > > { SYS_DESC(SYS_DBGPRCR_EL1), trap_raz_wi }, > > @@ -1930,7 +1949,7 @@ static const struct sys_reg_desc cp14_regs[] = { > > > > DBGBXVR(0), > > /* DBGOSLAR */ > > - { Op1( 0), CRn( 1), CRm( 0), Op2( 4), trap_raz_wi }, > > + { Op1( 0), CRn( 1), CRm( 0), Op2( 4), trap_oslar_el1 }, > > DBGBXVR(1), > > /* DBGOSLSR */ > > { Op1( 0), CRn( 1), CRm( 1), Op2( 4), trap_oslsr_el1, NULL, OSLSR_EL1 }, > > -- > > 2.33.1.1089.g2158813163f-goog > >