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[PAL/vm] Use etc/e820 fw_cfg file to learn reserved memory ranges #27

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dimakuv opened this issue May 6, 2024 · 0 comments · May be fixed by #28
Open

[PAL/vm] Use etc/e820 fw_cfg file to learn reserved memory ranges #27

dimakuv opened this issue May 6, 2024 · 0 comments · May be fixed by #28

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@dimakuv
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dimakuv commented May 6, 2024 •
edited

Currently, the VM PAL assumes hard-coded reserved memory ranges and does not consult the E820 memory table.

This worked in the previous QEMU versions (e.g. it works on 6.2.0), but fails on e.g. 8.0.4.

I did a pretty stupid hard-coding like this:

gramine-tdx/pal/src/host/vm/pal_main.c

Lines 173 to 175 in 8598f92

e820_table_entry e820 = { .address = 0x0,
.size = rdfwcfg(FW_CFG_RAM_SIZE, sizeof(uint64_t)),
.type = E820_ADDRESS_RANGE_MEMORY };

(Note that TDX PAL correctly constructs the E820 table from the info provided by the TDX hobs.)

So it looks like I should use the etc/e820 fw_cfg file from now on. This was introduced in 2013, so no issues with older QEMUs.

Moreover, I cannot use FW_CFG_E820_TABLE fw_cfg, as it was deprecated since 7.2.0.

TODO: implement /etc/e820 fw_cfg and reconstruct the bytes from QEMU into our data struct. See qemu/qemu@7d67110 for details.
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[PAL/vm-common] Get memory regions from VMM using "etc/e820" fw_cfg file gramineproject/gramine-tdx
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@dimakuv