Re: [PATCH v2 12/39] xen/riscv: implement vCPU context switching

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.09.2026 10:26, Baptiste Le Duc wrote:
>> @@ -329,6 +333,169 @@ int arch_domain_create(struct domain *d,
>>      return rc;
>>  }
>>  
>> +static void save_csr_regs(struct vcpu *vcpu)
>> +{
>> +    /*
>> +     * There is no need to save these CSRs as only hypervisor writes them in
>> +     * restore_csr_regs() and guest can't access them so they shouldn't be
>> +     * stored here. Keep them commented here just for symmetry with the
>> +     * restore CSRs register part.
>> +     *
>> +     * vcpu->arch.hedeleg = csr_read(CSR_HEDELEG);
>> +     * vcpu->arch.hideleg = csr_read(CSR_HIDELEG);
>> +     * vcpu->arch.henvcfg = csr_read64(CSR_HENVCFG);
>> +     * vcpu->arch.hcounteren = csr_read(CSR_HCOUNTEREN);
>> +     * vcpu->arch.htimedelta = csr_read64(CSR_HTIMEDELTA);
>> +     *
>> +     * if ( riscv_isa_extension_available(NULL, RISCV_ISA_EXT_smstateen) )
>> +     *     vcpu->arch.hstateen0 = csr_read(CSR_HSTATEEN0);
>> +     */
>> +
>> +    vcpu->arch.hvip = csr_read(CSR_HVIP);
>> +
>> +    vcpu->arch.vsstatus = csr_read(CSR_VSSTATUS);
>> +    vcpu->arch.vsie = csr_read(CSR_VSIE);
> 
> 
>> +    vcpu->arch.vstvec = csr_read(CSR_VSTVEC);
>> +    vcpu->arch.vsscratch = csr_read(CSR_VSSCRATCH);
>> +    vcpu->arch.vscause = csr_read(CSR_VSCAUSE);
>> +    vcpu->arch.vstval = csr_read(CSR_VSTVAL);
>> +    vcpu->arch.vsepc = csr_read(CSR_VSEPC);
>> +}
>> +
>> +static void restore_csr_regs(struct vcpu *vcpu)
>> +{
>> +    csr_write(CSR_HEDELEG, vcpu->arch.hedeleg);
>> +    csr_write(CSR_HIDELEG, vcpu->arch.hideleg);
>> +    csr_write(CSR_HVIP, vcpu->arch.hvip);
>> +    csr_write64(CSR_HENVCFG, vcpu->arch.henvcfg);
>> +    csr_write(CSR_HCOUNTEREN, vcpu->arch.hcounteren);
>> +    csr_write64(CSR_HTIMEDELTA, vcpu->arch.htimedelta);
>> +
>> +    if ( riscv_isa_extension_available(NULL, RISCV_ISA_EXT_smstateen) )
>> +        csr_write(CSR_HSTATEEN0, vcpu->arch.hstateen0);
>> +
>> +    csr_write(CSR_VSSTATUS, vcpu->arch.vsstatus);
>> +    csr_write(CSR_VSIE, vcpu->arch.vsie);
> 
> 
>> +    csr_write(CSR_VSTVEC, vcpu->arch.vstvec);
>> +    csr_write(CSR_VSSCRATCH, vcpu->arch.vsscratch);
>> +    csr_write(CSR_VSCAUSE, vcpu->arch.vscause);
>> +    csr_write(CSR_VSTVAL, vcpu->arch.vstval);
>> +    csr_write(CSR_VSEPC, vcpu->arch.vsepc);
>> +}
>> +
>> +static void ctxt_switch_from(struct vcpu *p)
> Is it expected to have diverse names for the vcpu arg? Above it's vcpu,
> here it's p (I assume it's for `previous` but I think the _from alone is
> enough to understand) and below it's n. Shouldn't be better to keep the same 
> name?

Context switch code is special, and using p and n can be warranted there.
Everywhere else it should be v, nothing else (and I said so to Oleksii
more than once before). Unless, of course, multiple vCPU-s come into play
at the same time.

Jan