Re: [PATCH v2 1/2] hw/nvme: add support for boot partiotions

[Stefan Hajnoczi]

On Tue, Jun 01, 2021 at 08:07:48PM +0530, Gollu Appalanaidu wrote:
> @@ -5546,6 +5665,47 @@ static void nvme_write_bar(NvmeCtrl *n, hwaddr offset, 
> uint64_t data,
>          NVME_GUEST_ERR(pci_nvme_ub_mmiowr_cmbsz_readonly,
>                         "invalid write to read only CMBSZ, ignored");
>          return;
> +    case 0x44:  /* BPRSEL */
> +        n->bar.bprsel = data & 0xffffffff;
> +        size_t bp_len = NVME_BPRSEL_BPRSZ(n->bar.bprsel) * 4 * KiB;
> +        int64_t bp_offset = NVME_BPRSEL_BPROF(n->bar.bprsel) * 4 * KiB;
> +        int64_t off = 0;
> +        struct nvme_bp_read_ctx *ctx;
> +
> +        trace_pci_nvme_mmio_bprsel(data, n->bar.bprsel,
> +                                   NVME_BPRSEL_BPID(n->bar.bpinfo),
> +                                   bp_offset, bp_len);
> +
> +        if (bp_len + bp_offset > n->bp_size) {
> +            NVME_BPINFO_CLEAR_BRS(n->bar.bpinfo);
> +            NVME_BPINFO_SET_BRS(n->bar.bpinfo, NVME_BPINFO_BRS_ERROR);
> +            return;
> +        }
> +
> +        off = NVME_BPRSEL_BPID(n->bar.bpinfo) * n->bp_size + bp_offset;
> +
> +        NVME_BPINFO_CLEAR_BRS(n->bar.bpinfo);
> +        NVME_BPINFO_SET_BRS(n->bar.bpinfo, NVME_BPINFO_BRS_READING);
> +
> +        ctx = g_new(struct nvme_bp_read_ctx, 1);
> +
> +        ctx->n = n;
> +
> +        pci_dma_sglist_init(&ctx->qsg, &n->parent_obj, 1);
> +
> +        qemu_sglist_add(&ctx->qsg, n->bar.bpmbl, bp_len);
> +
> +        dma_blk_read(n->blk_bp, &ctx->qsg, off , BDRV_SECTOR_SIZE,
> +                     nvme_bp_read_cb, ctx);

The returned BlockAIOCB is not stored. Two questions:

1. Can the guest allocate unbounded amounts of QEMU memory (struct
   nvme_bp_read_ctx) by repeatedly writing to this register?

2. What happens if the NVMe device is hot unplugged or reset while a
   boot partition read request is in flight?

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