Re: [RFC PATCH 05/19] kvm: Enable KVM_SET_USER_MEMORY_REGION2 for memslot

[Xiaoyao Li <xiaoyao.li@xxxxxxxxx>]

On 8/2/2023 1:10 AM, Claudio Fontana wrote:
> On 7/31/23 18:21, Xiaoyao Li wrote:
> > From: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> >
> > Switch to KVM_SET_USER_MEMORY_REGION2 when supported by KVM.
> >
> > With KVM_SET_USER_MEMORY_REGION2, QEMU can set up memory region that
> > backen'ed both by hva-based shared memory and gmem fd based private
> > memory.
> >
> > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> > Codeveloped-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > ---
> >   accel/kvm/kvm-all.c      | 57 +++++++++++++++++++++++++++++++++-------
> >   accel/kvm/trace-events   |  2 +-
> >   include/sysemu/kvm_int.h |  2 ++
> >   3 files changed, 51 insertions(+), 10 deletions(-)
> >
> > diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> > index d8eee405de24..7b1818334ba7 100644
> > --- a/accel/kvm/kvm-all.c
> > +++ b/accel/kvm/kvm-all.c
> > @@ -288,35 +288,68 @@ int kvm_physical_memory_addr_from_host(KVMState *s, void *ram,
> >   static int kvm_set_user_memory_region(KVMMemoryListener *kml, KVMSlot *slot, bool new)
> >   {
> >       KVMState *s = kvm_state;
> > -    struct kvm_userspace_memory_region mem;
> > +    struct kvm_userspace_memory_region2 mem;
> > +    static int cap_user_memory2 = -1;
> >       int ret;
> >   
> > +    if (cap_user_memory2 == -1) {
> > +        cap_user_memory2 = kvm_check_extension(s, KVM_CAP_USER_MEMORY2);
> > +    }
> > +
> > +    if (!cap_user_memory2 && slot->fd >= 0) {
> > +        error_report("%s, KVM doesn't support gmem!", __func__);
> > +        exit(1);
> > +    }
>
> We handle this special error case here,
> while the existing callers of kvm_set_user_memory_region handle the other error cases in different places.
>
> Not that the rest of kvm-all does an excellent job at error handling, but maybe we can avoid compounding on the issue.

I'm not sure how to align them. Do you have any suggestion?

> > +
> >       mem.slot = slot->slot | (kml->as_id << 16);
> >       mem.guest_phys_addr = slot->start_addr;
> >       mem.userspace_addr = (unsigned long)slot->ram;
> >       mem.flags = slot->flags;
> > +    mem.gmem_fd = slot->fd;
> > +    mem.gmem_offset = slot->ofs;
> >   
> > -    if (slot->memory_size && !new && (mem.flags ^ slot->old_flags) & KVM_MEM_READONLY) {
> > +    if (slot->memory_size && !new && (slot->flags ^ slot->old_flags) & KVM_MEM_READONLY) {
>
> Why the change if mem.flags == slot->flags ?

I guess the goal is to make it clearer that it's comparing the (new) 
flags with old_flags of the slot.

Anyway, if this change is annoying, I can drop it. :)

> >           /* Set the slot size to 0 before setting the slot to the desired
> >            * value. This is needed based on KVM commit 75d61fbc. */
> >           mem.memory_size = 0;
> > -        ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
> > +
> > +        if (cap_user_memory2) {
> > +            ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION2, &mem);
> > +        } else {
> > +            ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
> > +	    }
> >           if (ret < 0) {
> >               goto err;
> >           }
> >       }
> >       mem.memory_size = slot->memory_size;
> > -    ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
> > +    if (cap_user_memory2) {
> > +        ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION2, &mem);
> > +    } else {
> > +        ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
> > +    }
> >       slot->old_flags = mem.flags;
> >   err:
> >       trace_kvm_set_user_memory(mem.slot >> 16, (uint16_t)mem.slot, mem.flags,
> >                                 mem.guest_phys_addr, mem.memory_size,
> > -                              mem.userspace_addr, ret);
> > +                              mem.userspace_addr, mem.gmem_fd,
> > +			      mem.gmem_offset, ret);
> >       if (ret < 0) {
> > -        error_report("%s: KVM_SET_USER_MEMORY_REGION failed, slot=%d,"
> > -                     " start=0x%" PRIx64 ", size=0x%" PRIx64 ": %s",
> > -                     __func__, mem.slot, slot->start_addr,
> > -                     (uint64_t)mem.memory_size, strerror(errno));
> > +        if (cap_user_memory2) {
> > +                error_report("%s: KVM_SET_USER_MEMORY_REGION2 failed, slot=%d,"
> > +                        " start=0x%" PRIx64 ", size=0x%" PRIx64 ","
> > +                        " flags=0x%" PRIx32 ","
> > +                        " gmem_fd=%" PRId32 ", gmem_offset=0x%" PRIx64 ": %s",
> > +                        __func__, mem.slot, slot->start_addr,
> > +                (uint64_t)mem.memory_size, mem.flags,
> > +                        mem.gmem_fd, (uint64_t)mem.gmem_offset,
> > +                        strerror(errno));
> > +        } else {
> > +                error_report("%s: KVM_SET_USER_MEMORY_REGION failed, slot=%d,"
> > +                            " start=0x%" PRIx64 ", size=0x%" PRIx64 ": %s",
> > +                __func__, mem.slot, slot->start_addr,
> > +                (uint64_t)mem.memory_size, strerror(errno));
> > +        }
> >       }
> >       return ret;
> >   }
> > @@ -472,6 +505,9 @@ static int kvm_mem_flags(MemoryRegion *mr)
> >       if (readonly && kvm_readonly_mem_allowed) {
> >           flags |= KVM_MEM_READONLY;
> >       }
> > +    if (memory_region_can_be_private(mr)) {
> > +        flags |= KVM_MEM_PRIVATE;
> > +    }
> >       return flags;
> >   }
> >   
> > @@ -1402,6 +1438,9 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
> >           mem->ram_start_offset = ram_start_offset;
> >           mem->ram = ram;
> >           mem->flags = kvm_mem_flags(mr);
> > +        mem->fd = mr->ram_block->gmem_fd;
> > +        mem->ofs = (uint8_t*)ram - mr->ram_block->host;
> > +
> >           kvm_slot_init_dirty_bitmap(mem);
> >           err = kvm_set_user_memory_region(kml, mem, true);
> >           if (err) {
> > diff --git a/accel/kvm/trace-events b/accel/kvm/trace-events
> > index 14ebfa1b991c..80694683acea 100644
> > --- a/accel/kvm/trace-events
> > +++ b/accel/kvm/trace-events
> > @@ -15,7 +15,7 @@ kvm_irqchip_update_msi_route(int virq) "Updating MSI route virq=%d"
> >   kvm_irqchip_release_virq(int virq) "virq %d"
> >   kvm_set_ioeventfd_mmio(int fd, uint64_t addr, uint32_t val, bool assign, uint32_t size, bool datamatch) "fd: %d @0x%" PRIx64 " val=0x%x assign: %d size: %d match: %d"
> >   kvm_set_ioeventfd_pio(int fd, uint16_t addr, uint32_t val, bool assign, uint32_t size, bool datamatch) "fd: %d @0x%x val=0x%x assign: %d size: %d match: %d"
> > -kvm_set_user_memory(uint16_t as, uint16_t slot, uint32_t flags, uint64_t guest_phys_addr, uint64_t memory_size, uint64_t userspace_addr, int ret) "AddrSpace#%d Slot#%d flags=0x%x gpa=0x%"PRIx64 " size=0x%"PRIx64 " ua=0x%"PRIx64 " ret=%d"
> > +kvm_set_user_memory(uint16_t as, uint16_t slot, uint32_t flags, uint64_t guest_phys_addr, uint64_t memory_size, uint64_t userspace_addr, uint32_t fd, uint64_t fd_offset, int ret) "AddrSpace#%d Slot#%d flags=0x%x gpa=0x%"PRIx64 " size=0x%"PRIx64 " ua=0x%"PRIx64 " gmem_fd=%d" " gmem_fd_offset=0x%" PRIx64 " ret=%d"
> >   kvm_clear_dirty_log(uint32_t slot, uint64_t start, uint32_t size) "slot#%"PRId32" start 0x%"PRIx64" size 0x%"PRIx32
> >   kvm_resample_fd_notify(int gsi) "gsi %d"
> >   kvm_dirty_ring_full(int id) "vcpu %d"
> > diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
> > index 511b42bde5c4..48220c0793ac 100644
> > --- a/include/sysemu/kvm_int.h
> > +++ b/include/sysemu/kvm_int.h
> > @@ -30,6 +30,8 @@ typedef struct KVMSlot
> >       int as_id;
> >       /* Cache of the offset in ram address space */
> >       ram_addr_t ram_start_offset;
> > +    int fd;
> > +    hwaddr ofs;
> >   } KVMSlot;
> >   
> >   typedef struct KVMMemoryUpdate {