Hi Palmer, On Fri, Aug 12, 2022 at 3:19 AM Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote: > > On Fri, 22 Jul 2022 21:47:06 PDT (-0700), anup@xxxxxxxxxxxxxx wrote: > > Hi Palmer, > > > > On Fri, Jul 22, 2022 at 10:20 PM Atish Patra <atishp@xxxxxxxxxxxx> wrote: > >> > >> This series implements Sstc extension support which was ratified recently. > >> Before the Sstc extension, an SBI call is necessary to generate timer > >> interrupts as only M-mode have access to the timecompare registers. Thus, > >> there is significant latency to generate timer interrupts at kernel. > >> For virtualized enviornments, its even worse as the KVM handles the SBI call > >> and uses a software timer to emulate the timecomapre register. > >> > >> Sstc extension solves both these problems by defining a stimecmp/vstimecmp > >> at supervisor (host/guest) level. It allows kernel to program a timer and > >> recieve interrupt without supervisor execution enviornment (M-mode/HS mode) > >> intervention. > >> > >> KVM directly updates the vstimecmp as well if the guest kernel invokes the SBI > >> call instead of updating stimecmp directly. This is required because KVM will > >> enable sstc extension if the hardware supports it unless the VMM explicitly > >> disables it for that guest. The hardware is expected to compare the > >> vstimecmp at every cycle if sstc is enabled and any stale value in vstimecmp > >> will lead to spurious timer interrupts. This also helps maintaining the > >> backward compatibility with older kernels. > >> > >> Similary, the M-mode firmware(OpenSBI) uses stimecmp for older kernel > >> without sstc support as STIP bit in mip is read only for hardware with sstc. > >> > >> The PATCH 1 & 2 enables the basic infrastructure around Sstc extension while > >> PATCH 3 lets kernel use the Sstc extension if it is available in hardware. > >> PATCH 4 implements the Sstc extension in KVM. > >> > >> This series has been tested on Qemu(RV32 & RV64) with additional patches in > >> Qemu[2]. This series can also be found at [3]. > >> > >> Changes from v6->v7: > >> 1. Fixed a compilation error reported by 0-day bot. > >> > >> Changes from v5->v6: > >> 1. Moved SSTC extension enum below SVPBMT. > >> > >> Changes from v4->v5: > >> 1. Added RB tag. > >> 2. Changed the pr-format. > >> 3. Rebased on 5.19-rc7 and kvm-queue. > >> 4. Moved the henvcfg modification from hardware enable to vcpu_load. > >> > >> Changes from v3->v4: > >> 1. Rebased on 5.18-rc6 > >> 2. Unified vstimemp & next_cycles. > >> 3. Addressed comments in PATCH 3 & 4. > >> > >> Changes from v2->v3: > >> 1. Dropped unrelated KVM fixes from this series. > >> 2. Rebased on 5.18-rc3. > >> > >> Changes from v1->v2: > >> 1. Separate the static key from kvm usage > >> 2. Makde the sstc specific static key local to the driver/clocksource > >> 3. Moved the vstimecmp update code to the vcpu_timer > >> 4. Used function pointers instead of static key to invoke vstimecmp vs > >> hrtimer at the run time. This will help in future for migration of vms > >> from/to sstc enabled hardware to non-sstc enabled hardware. > >> 5. Unified the vstimer & timer to 1 timer as only one of them will be used > >> at runtime. > >> > >> [1] https://drive.google.com/file/d/1m84Re2yK8m_vbW7TspvevCDR82MOBaSX/view > >> [2] https://github.com/atishp04/qemu/tree/sstc_v6 > >> [3] https://github.com/atishp04/linux/tree/sstc_v7 > >> > >> Atish Patra (4): > >> RISC-V: Add SSTC extension CSR details > >> RISC-V: Enable sstc extension parsing from DT > >> RISC-V: Prefer sstc extension if available > >> RISC-V: KVM: Support sstc extension > > > > The PATCH4 is dependent on the KVM patches in queue for 5.20. > > > > I suggest you take PATCH1, PATCH2 and PATCH3. I will send > > PATCH4 in second batch/PR for 5.20 assuming you will send the > > first three patches in your first PR for 5.20 > > > > Does this sound okay to you ? > > Sorry for being slow here, I just merged the non-KVM ones onto > riscv/for-next. LMK if you want me to try and sort out the KVM bits, > the branch base is at palmer/riscv-sstc assuming that's easier for you > to just merge in locally. The KVM RISC-V changes for 5.20 are already merged in Linus's master so please go ahead and merge the KVM Sstc patch (i.e. PATCH4 of this series) in riscv/for-next with "Acked-by: Anup Patel <anup@xxxxxxxxxxxxxx>" Thanks, Anup > > > > > Regards, > > Anup > > > >> > >> arch/riscv/include/asm/csr.h | 5 + > >> arch/riscv/include/asm/hwcap.h | 1 + > >> arch/riscv/include/asm/kvm_vcpu_timer.h | 7 ++ > >> arch/riscv/include/uapi/asm/kvm.h | 1 + > >> arch/riscv/kernel/cpu.c | 1 + > >> arch/riscv/kernel/cpufeature.c | 1 + > >> arch/riscv/kvm/vcpu.c | 8 +- > >> arch/riscv/kvm/vcpu_timer.c | 144 +++++++++++++++++++++++- > >> drivers/clocksource/timer-riscv.c | 25 +++- > >> 9 files changed, 185 insertions(+), 8 deletions(-) > >> > >> -- > >> 2.25.1 > >>
