Re: [PATCH bpf-next v2 3/3] bpf, riscv: use prog pack allocator in the BPF JIT

Puranjay Mohan
2023-08-28T09:14:48Z

Hi Pu,

On Sat, Aug 26, 2023 at 3:36 AM Pu Lehui <pulehui@huawei.com> wrote:
>
>
>
> On 2023/8/25 19:40, Puranjay Mohan wrote:
> > Hi Pu,
> >
> > On Fri, Aug 25, 2023 at 1:12 PM Pu Lehui <pulehui@huawei.com> wrote:
> >>
> >>
> >>
> >> On 2023/8/25 16:42, Puranjay Mohan wrote:
> >>> Hi Pu,
> >>>
> >>> On Fri, Aug 25, 2023 at 9:34 AM Pu Lehui <pulehui@huawei.com> wrote:
> >>>>
> >>>>
> >>>>
> >>>> On 2023/8/25 15:09, Pu Lehui wrote:
> >>>>> Hi Puranjay,
> >>>>>
> >>>>> Happy to see the RV64 pack allocator implementation.
> >>>>
> >>>> RV32 also
> >>>>
> >>>>>
> >>>>> On 2023/8/24 21:31, Puranjay Mohan wrote:
> >>>>>> Use bpf_jit_binary_pack_alloc() for memory management of JIT binaries in
> >>>>>> RISCV BPF JIT. The bpf_jit_binary_pack_alloc creates a pair of RW and RX
> >>>>>> buffers. The JIT writes the program into the RW buffer. When the JIT is
> >>>>>> done, the program is copied to the final RX buffer with
> >>>>>> bpf_jit_binary_pack_finalize.
> >>>>>>
> >>>>>> Implement bpf_arch_text_copy() and bpf_arch_text_invalidate() for RISCV
> >>>>>> JIT as these functions are required by bpf_jit_binary_pack allocator.
> >>>>>>
> >>>>>> Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
> >>>>>> ---
> >>>>>> arch/riscv/net/bpf_jit.h | 3 +
> >>>>>> arch/riscv/net/bpf_jit_comp64.c | 56 +++++++++++++---
> >>>>>> arch/riscv/net/bpf_jit_core.c | 113 +++++++++++++++++++++++++++-----
> >>>>>> 3 files changed, 146 insertions(+), 26 deletions(-)
> >>>>>>
> >>>>>> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
> >>>>>> index 2717f5490428..ad69319c8ea7 100644
> >>>>>> --- a/arch/riscv/net/bpf_jit.h
> >>>>>> +++ b/arch/riscv/net/bpf_jit.h
> >>>>>> @@ -68,6 +68,7 @@ static inline bool is_creg(u8 reg)
> >>>>>> struct rv_jit_context {
> >>>>>> struct bpf_prog *prog;
> >>>>>> u16 *insns; /* RV insns */
> >>>>>> + u16 *ro_insns;
> >>>>
> >>>> In fact, the definition of w/ or w/o ro_ still looks a bit confusing.
> >>>> Maybe it is better for us not to change the current framework, as the
> >>>> current `image` is the final executed RX image, and the trampoline
> >>>> treats `image` as the same. Maybe it would be better to add a new RW
> >>>> image, such like `rw_iamge`, so that we do not break the existing
> >>>> framework and do not have to add too many comments.
> >>>
> >>> I had thought about this and decided to create a new _ro image/header
> >>> and not _rw image/header. Here is my reasoning:
> >>> If we let the existing insns, header be considered the read_only
> >>> version from where the
> >>> program will run, and create new rw_insn and rw_header for doing the jit process
> >>> it would require a lot more changes to the framework.
> >>> functions like build_body(), bpf_jit_build_prologue(), etc. work on
> >>> ctx->insns and
> >>
> >> Hmm, the other parts should be fine, but the emit instruction is a
> >> problem. All right, let's go ahead.
> >>
> >>> now all these references would have to be changed to ctx->rw_insns.
> >>>
> >>> Howsoever we implement this, there is no way to do it without changing
> >>> the current framework.
> >>> The crux of the problem is that we need to use the r/w area for
> >>> writing and the r/x area for calculating
> >>> offsets.
> >>>
> >>> If you think this can be done in a more efficient way then I would
> >>> love to implement that, but all other
> >>> solutions that I tried made the code very difficult to follow.
> >>>
> >>>>
> >>>> And any other parts, it looks great.😄
> >>>>
> >>>>>> int ninsns;
> >>>>>> int prologue_len;
> >>>>>> int epilogue_offset;
> >>>>>> @@ -85,7 +86,9 @@ static inline int ninsns_rvoff(int ninsns)
> >>>>>> struct rv_jit_data {
> >>>>>> struct bpf_binary_header *header;
> >>>>>> + struct bpf_binary_header *ro_header;
> >>>>>> u8 *image;
> >>>>>> + u8 *ro_image;
> >>>>>> struct rv_jit_context ctx;
> >>>>>> };
> >>>>>> diff --git a/arch/riscv/net/bpf_jit_comp64.c
> >>>>>> b/arch/riscv/net/bpf_jit_comp64.c
> >>>>>> index 0ca4f5c0097c..d77b16338ba2 100644
> >>>>>> --- a/arch/riscv/net/bpf_jit_comp64.c
> >>>>>> +++ b/arch/riscv/net/bpf_jit_comp64.c
> >>>>>> @@ -144,7 +144,11 @@ static bool in_auipc_jalr_range(s64 val)
> >>>>>> /* Emit fixed-length instructions for address */
> >>>>>> static int emit_addr(u8 rd, u64 addr, bool extra_pass, struct
> >>>>>> rv_jit_context *ctx)
> >>>>>> {
> >>>>>> - u64 ip = (u64)(ctx->insns + ctx->ninsns);
> >>>>>> + /*
> >>>>>> + * Use the ro_insns(RX) to calculate the offset as the BPF
> >>>>>> program will
> >>>>>> + * finally run from this memory region.
> >>>>>> + */
> >>>>>> + u64 ip = (u64)(ctx->ro_insns + ctx->ninsns);
> >>>>>> s64 off = addr - ip;
> >>>>>> s64 upper = (off + (1 << 11)) >> 12;
> >>>>>> s64 lower = off & 0xfff;
> >>>>>> @@ -465,7 +469,11 @@ static int emit_call(u64 addr, bool fixed_addr,
> >>>>>> struct rv_jit_context *ctx)
> >>>>>> u64 ip;
> >>>>>> if (addr && ctx->insns) {
> >>>>>
> >>>>> ctx->insns need to sync to ctx->ro_insns
> >>>
> >>> Can you elaborate this more. I am missing something here.
> >>> The sync happens at the end by calling bpf_jit_binary_pack_finalize().
> >>
> >> if (addr && ctx->insns) {
> >> ip = (u64)(long)(ctx->ro_insns + ctx->ninsns);
> >> off = addr - ip;
> >> }
> >> emit ctx->insns + off
> >>
> >> Here we are assuming ctx->insns == ctx->ro_insns, if they not, the
> >> offset calculated by ctx->ro_insns will not meaningful for ctx->insns.
> >
> > We are not assuming that ctx->insns == ctx->ro_insns at this point.
> > We are just finding the offset: off = addr(let's say in kernel) -
> > ip(address of the instruction);
> >
> >> I was curious why we need to use ro_insns to calculate offset? Is that
> >> any problem if we do jit iteration with ctx->insns and the final copy
> >> ctx->insns to ro_insns?
> >
> > All the offsets within the image can be calculated using ctx->insns and it will
> > work but if the emit_call() is for an address in the kernel code let's
> > say, then the
> > offset between this address(in kernel) and the R/W image would be different from
> > the offset between the address(in kernel) and the R/O image.
> > We need the offset between the R/X Image and the kernel address. Because the
> > CPU will execute the instructions from there.
>
> Agree with that, thanks for explaination. Let's talk about my original
> idea, shall we add check like this to reject ctx->ro_insns == NULL?
>
> if (addr && ctx->insns && ctx->ro_insns) {
> ...
> }

Will add in the next version.

>
> >
> >>
> >>>
> >>>>>
> >>>>>> - ip = (u64)(long)(ctx->insns + ctx->ninsns);
> >>>>>> + /*
> >>>>>> + * Use the ro_insns(RX) to calculate the offset as the BPF
> >>>>>> + * program will finally run from this memory region.
> >>>>>> + */
> >>>>>> + ip = (u64)(long)(ctx->ro_insns + ctx->ninsns);
> >>>>>> off = addr - ip;
> >>>>>> }
> >>>>>> @@ -578,7 +586,8 @@ static int add_exception_handler(const struct
> >>>>>> bpf_insn *insn,
> >>>>>> {
> >>>>>> struct exception_table_entry *ex;
> >>>>>> unsigned long pc;
> >>>>>> - off_t offset;
> >>>>>> + off_t ins_offset;
> >>>>>> + off_t fixup_offset;
> >>>>>> if (!ctx->insns || !ctx->prog->aux->extable ||
> >>>>>> BPF_MODE(insn->code) != BPF_PROBE_MEM)
> >>>>>
> >>>>> ctx->ro_insns need to be checked also.
> >>>
> >>> ctx->ro_insns is not initialised until we call bpf_jit_binary_pack_finalize()?
> >
> > ctx->ro_insns and ctx->insns are both allocated together by
> > bpf_jit_binary_pack_alloc().
> > ctx->ro_insns is marked R/X and ctx->insns is marked R/W. We dump all
> > instructions in
> > ctx->insns and then copy them to ctx->ro_insns with
> > bpf_jit_binary_pack_finalize().
> >
> > The catch is that instructions that work with offsets like JAL need
> > the offsets from ctx->ro_insns.
> > as explained above.
> >
> >>
> >> if (!ctx->insns || !ctx->prog->aux->extable ||
> >> ...
> >> pc = (unsigned long)&ctx->ro_insns[ctx->ninsns - insn_len];
>
> Also here, to add check like this to reject ctx->ro_insns == NULL which
> may cause null pointer dereference?
>
> if (!ctx->insns || !ctx->ro_insns || !ctx->prog->aux->extable ||

Will add in next version.

>
> >>
> >> The uninitialized ctx->ro_insns may lead to illegal address access.
> >> Although it will never happen, because we also assume that ctx->insns ==
> >> ctx->ro_insns.
> >
> > Here also we are not assuming ctx->insns == ctx->ro_insns. The ctx->ro_insns is
> > allocated but not initialised yet. So all addresses in range
> > ctx->ro_insns to ctx->ro_insns + size
> > are valid addresses. Here we are using the addresses only to find the
> > offset and not accessing those
> > addresses.
> >
> >>
> >>>
> >>>>>
> >>>>>> return 0;
> >>>>>> @@ -593,12 +602,17 @@ static int add_exception_handler(const struct
> >>>>>> bpf_insn *insn,
> >>>>>> return -EINVAL;
> >>>>>> ex = &ctx->prog->aux->extable[ctx->nexentries];
> >>>>>> - pc = (unsigned long)&ctx->insns[ctx->ninsns - insn_len];
> >>>>>> + pc = (unsigned long)&ctx->ro_insns[ctx->ninsns - insn_len];
> >>>>>> - offset = pc - (long)&ex->insn;
> >>>>>> - if (WARN_ON_ONCE(offset >= 0 || offset < INT_MIN))
> >>>>>> + /*
> >>>>>> + * This is the relative offset of the instruction that may fault
> >>>>>> from
> >>>>>> + * the exception table itself. This will be written to the exception
> >>>>>> + * table and if this instruction faults, the destination register
> >>>>>> will
> >>>>>> + * be set to '0' and the execution will jump to the next
> >>>>>> instruction.
> >>>>>> + */
> >>>>>> + ins_offset = pc - (long)&ex->insn;
> >>>>>> + if (WARN_ON_ONCE(ins_offset >= 0 || ins_offset < INT_MIN))
> >>>>>> return -ERANGE;
> >>>>>> - ex->insn = offset;
> >>>>>> /*
> >>>>>> * Since the extable follows the program, the fixup offset is
> >>>>>> always
> >>>>>> @@ -607,12 +621,25 @@ static int add_exception_handler(const struct
> >>>>>> bpf_insn *insn,
> >>>>>> * bits. We don't need to worry about buildtime or runtime sort
> >>>>>> * modifying the upper bits because the table is already sorted,
> >>>>>> and
> >>>>>> * isn't part of the main exception table.
> >>>>>> + *
> >>>>>> + * The fixup_offset is set to the next instruction from the
> >>>>>> instruction
> >>>>>> + * that may fault. The execution will jump to this after handling
> >>>>>> the
> >>>>>> + * fault.
> >>>>>> */
> >>>>>> - offset = (long)&ex->fixup - (pc + insn_len * sizeof(u16));
> >>>>>> - if (!FIELD_FIT(BPF_FIXUP_OFFSET_MASK, offset))
> >>>>>> + fixup_offset = (long)&ex->fixup - (pc + insn_len * sizeof(u16));
> >>>>>> + if (!FIELD_FIT(BPF_FIXUP_OFFSET_MASK, fixup_offset))
> >>>>>> return -ERANGE;
> >>>>>> - ex->fixup = FIELD_PREP(BPF_FIXUP_OFFSET_MASK, offset) |
> >>>>>> + /*
> >>>>>> + * The offsets above have been calculated using the RO buffer but we
> >>>>>> + * need to use the R/W buffer for writes.
> >>>>>> + * switch ex to rw buffer for writing.
> >>>>>> + */
> >>>>>> + ex = (void *)ctx->insns + ((void *)ex - (void *)ctx->ro_insns);
> >>>>>> +
> >>>>>> + ex->insn = ins_offset;
> >>>>>> +
> >>>>>> + ex->fixup = FIELD_PREP(BPF_FIXUP_OFFSET_MASK, fixup_offset) |
> >>>>>> FIELD_PREP(BPF_FIXUP_REG_MASK, dst_reg);
> >>>>>> ex->type = EX_TYPE_BPF;
> >>>>>> @@ -1006,6 +1033,7 @@ int arch_prepare_bpf_trampoline(struct
> >>>>>> bpf_tramp_image *im, void *image,
> >>>>>> ctx.ninsns = 0;
> >>>>>> ctx.insns = NULL;
> >>>>>> + ctx.ro_insns = NULL;
> >>>>>> ret = __arch_prepare_bpf_trampoline(im, m, tlinks, func_addr,
> >>>>>> flags, &ctx);
> >>>>>> if (ret < 0)
> >>>>>> return ret;
> >>>>>> @@ -1014,7 +1042,15 @@ int arch_prepare_bpf_trampoline(struct
> >>>>>> bpf_tramp_image *im, void *image,
> >>>>>> return -EFBIG;
> >>>>>> ctx.ninsns = 0;
> >>>>>> + /*
> >>>>>> + * The bpf_int_jit_compile() uses a RW buffer (ctx.insns) to
> >>>>>> write the
> >>>>>> + * JITed instructions and later copies it to a RX region
> >>>>>> (ctx.ro_insns).
> >>>>>> + * It also uses ctx.ro_insns to calculate offsets for jumps etc.
> >>>>>> As the
> >>>>>> + * trampoline image uses the same memory area for writing and
> >>>>>> execution,
> >>>>>> + * both ctx.insns and ctx.ro_insns can be set to image.
> >>>>>> + */
> >>>>>> ctx.insns = image;
> >>>>>> + ctx.ro_insns = image;
> >>>>>> ret = __arch_prepare_bpf_trampoline(im, m, tlinks, func_addr,
> >>>>>> flags, &ctx);
> >>>>>> if (ret < 0)
> >>>>>> return ret;
> >>>>>> diff --git a/arch/riscv/net/bpf_jit_core.c
> >>>>>> b/arch/riscv/net/bpf_jit_core.c
> >>>>>> index 7a26a3e1c73c..4c8dffc09368 100644
> >>>>>> --- a/arch/riscv/net/bpf_jit_core.c
> >>>>>> +++ b/arch/riscv/net/bpf_jit_core.c
> >>>>>> @@ -8,6 +8,8 @@
> >>>>>> #include <linux/bpf.h>
> >>>>>> #include <linux/filter.h>
> >>>>>> +#include <linux/memory.h>
> >>>>>> +#include <asm/patch.h>
> >>>>>> #include "bpf_jit.h"
> >>>>>> /* Number of iterations to try until offsets converge. */
> >>>>>> @@ -117,16 +119,27 @@ struct bpf_prog *bpf_int_jit_compile(struct
> >>>>>> bpf_prog *prog)
> >>>>>> sizeof(struct exception_table_entry);
> >>>>>> prog_size = sizeof(*ctx->insns) * ctx->ninsns;
> >>>>>> - jit_data->header =
> >>>>>> - bpf_jit_binary_alloc(prog_size + extable_size,
> >>>>>> - &jit_data->image,
> >>>>>> - sizeof(u32),
> >>>>>> - bpf_fill_ill_insns);
> >>>>>> - if (!jit_data->header) {
> >>>>>> + jit_data->ro_header =
> >>>>>> + bpf_jit_binary_pack_alloc(prog_size +
> >>>>>> + extable_size,
> >>>>>> + &jit_data->ro_image,
> >>>>>> + sizeof(u32),
> >>>>>> + &jit_data->header,
> >>>>>> + &jit_data->image,
> >>>>>> + bpf_fill_ill_insns);
> >>>>>> + if (!jit_data->ro_header) {
> >>>>>> prog = orig_prog;
> >>>>>> goto out_offset;
> >>>>>> }
> >>>>>> + /*
> >>>>>> + * Use the image(RW) for writing the JITed instructions.
> >>>>>> But also save
> >>>>>> + * the ro_image(RX) for calculating the offsets in the
> >>>>>> image. The RW
> >>>>>> + * image will be later copied to the RX image from where
> >>>>>> the program
> >>>>>> + * will run. The bpf_jit_binary_pack_finalize() will do
> >>>>>> this copy in the
> >>>>>> + * final step.
> >>>>>> + */
> >>>>>> + ctx->ro_insns = (u16 *)jit_data->ro_image;
> >>>>>> ctx->insns = (u16 *)jit_data->image;
> >>>>>> /*
> >>>>>> * Now, when the image is allocated, the image can
> >>>>>> @@ -138,14 +151,12 @@ struct bpf_prog *bpf_int_jit_compile(struct
> >>>>>> bpf_prog *prog)
> >>>>>> if (i == NR_JIT_ITERATIONS) {
> >>>>>> pr_err("bpf-jit: image did not converge in <%d passes!\n", i);
> >>>>>> - if (jit_data->header)
> >>>>>> - bpf_jit_binary_free(jit_data->header);
> >>>>>> prog = orig_prog;
> >>>>>> - goto out_offset;
> >>>>>> + goto out_free_hdr;
> >>>>>> }
> >>>>>> if (extable_size)
> >>>>>> - prog->aux->extable = (void *)ctx->insns + prog_size;
> >>>>>> + prog->aux->extable = (void *)ctx->ro_insns + prog_size;
> >>>>>> skip_init_ctx:
> >>>>>> pass++;
> >>>>>> @@ -154,23 +165,35 @@ struct bpf_prog *bpf_int_jit_compile(struct
> >>>>>> bpf_prog *prog)
> >>>>>> bpf_jit_build_prologue(ctx);
> >>>>>> if (build_body(ctx, extra_pass, NULL)) {
> >>>>>> - bpf_jit_binary_free(jit_data->header);
> >>>>>> prog = orig_prog;
> >>>>>> - goto out_offset;
> >>>>>> + goto out_free_hdr;
> >>>>>> }
> >>>>>> bpf_jit_build_epilogue(ctx);
> >>>>>> if (bpf_jit_enable > 1)
> >>>>>> bpf_jit_dump(prog->len, prog_size, pass, ctx->insns);
> >>>>>> - prog->bpf_func = (void *)ctx->insns;
> >>>>>> + prog->bpf_func = (void *)ctx->ro_insns;
> >>>>>> prog->jited = 1;
> >>>>>> prog->jited_len = prog_size;
> >>>>>> - bpf_flush_icache(jit_data->header, ctx->insns + ctx->ninsns);
> >>>>>> -
> >>>>>> if (!prog->is_func || extra_pass) {
> >>>>>> - bpf_jit_binary_lock_ro(jit_data->header);
> >>>>>> + if (WARN_ON(bpf_jit_binary_pack_finalize(prog,
> >>>>>> + jit_data->ro_header,
> >>>>>> + jit_data->header))) {
> >>>>>> + /* ro_header has been freed */
> >>>>>> + jit_data->ro_header = NULL;
> >>>>>> + prog = orig_prog;
> >>>>>> + goto out_offset;
> >>>>>> + }
> >>>>>> + /*
> >>>>>> + * The instructions have now been copied to the ROX region from
> >>>>>> + * where they will execute.
> >>>>>> + * Write any modified data cache blocks out to memory and
> >>>>>> + * invalidate the corresponding blocks in the instruction cache.
> >>>>>> + */
> >>>>>> + bpf_flush_icache(jit_data->ro_header,
> >>>>>> + ctx->ro_insns + ctx->ninsns);
> >>>>>> for (i = 0; i < prog->len; i++)
> >>>>>> ctx->offset[i] = ninsns_rvoff(ctx->offset[i]);
> >>>>>> bpf_prog_fill_jited_linfo(prog, ctx->offset);
> >>>>>> @@ -185,6 +208,15 @@ struct bpf_prog *bpf_int_jit_compile(struct
> >>>>>> bpf_prog *prog)
> >>>>>> bpf_jit_prog_release_other(prog, prog == orig_prog ?
> >>>>>> tmp : orig_prog);
> >>>>>> return prog;
> >>>>>> +
> >>>>>> +out_free_hdr:
> >>>>>> + if (jit_data->header) {
> >>>>>> + bpf_arch_text_copy(&jit_data->ro_header->size,
> >>>>>> + &jit_data->header->size,
> >>>>>> + sizeof(jit_data->header->size));
> >>>>>> + bpf_jit_binary_pack_free(jit_data->ro_header, jit_data->header);
> >>>>>> + }
> >>>>>> + goto out_offset;
> >>>>>> }
> >>>>>> u64 bpf_jit_alloc_exec_limit(void)
> >>>>>> @@ -204,3 +236,52 @@ void bpf_jit_free_exec(void *addr)
> >>>>>> {
> >>>>>> return vfree(addr);
> >>>>>> }
> >>>>>> +
> >>>>>> +void *bpf_arch_text_copy(void *dst, void *src, size_t len)
> >>>>>> +{
> >>>>>> + int ret;
> >>>>>> +
> >>>>>> + mutex_lock(&text_mutex);
> >>>>>> + ret = patch_text_nosync(dst, src, len);
> >>>>>> + mutex_unlock(&text_mutex);
> >>>>>> +
> >>>>>> + if (ret)
> >>>>>> + return ERR_PTR(-EINVAL);
> >>>>>> +
> >>>>>> + return dst;
> >>>>>> +}
> >>>>>> +
> >>>>>> +int bpf_arch_text_invalidate(void *dst, size_t len)
> >>>>>> +{
> >>>>>> + int ret = 0;
> >>>>>
> >>>>> no need to initialize it
> >>>>>
> >>>>>> +
> >>>>>> + mutex_lock(&text_mutex);
> >>>>>> + ret = patch_text_set_nosync(dst, 0, len);
> >>>>>> + mutex_unlock(&text_mutex);
> >>>>>> +
> >>>>>> + return ret;
> >>>>>> +}
> >>>>>> +
> >>>>>> +void bpf_jit_free(struct bpf_prog *prog)
> >>>>>> +{
> >>>>>> + if (prog->jited) {
> >>>>>> + struct rv_jit_data *jit_data = prog->aux->jit_data;
> >>>>>> + struct bpf_binary_header *hdr;
> >>>>>> +
> >>>>>> + /*
> >>>>>> + * If we fail the final pass of JIT (from jit_subprogs),
> >>>>>> + * the program may not be finalized yet. Call finalize here
> >>>>>> + * before freeing it.
> >>>>>> + */
> >>>>>> + if (jit_data) {
> >>>>>> + bpf_jit_binary_pack_finalize(prog, jit_data->ro_header,
> >>>>>> + jit_data->header);
> >>>>>> + kfree(jit_data);
> >>>>>> + }
> >>>>>> + hdr = bpf_jit_binary_pack_hdr(prog);
> >>>>>> + bpf_jit_binary_pack_free(hdr, NULL);
> >>>>>> + WARN_ON_ONCE(!bpf_prog_kallsyms_verify_off(prog));
> >>>>>> + }
> >>>>>> +
> >>>>>> + bpf_prog_unlock_free(prog);
> >>>>>> +}
> >>>>>
> >>>>>
> >>>
> >>> Thanks,
> >>> Puranjay
> >
> >
> > Thanks,
> > Puranjay

--
Thanks and Regards

Yours Truly,

Puranjay Mohan