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Re: [PATCH v3 1/1] target/i386: Enable page walking from MMIO memory


From: Richard Henderson
Subject: Re: [PATCH v3 1/1] target/i386: Enable page walking from MMIO memory
Date: Wed, 20 Mar 2024 16:34:03 -1000
User-agent: Mozilla Thunderbird

Paolo, ping!

On 3/13/24 09:30, Richard Henderson wrote:
On 3/7/24 05:53, Jonathan Cameron wrote:
From: Gregory Price <gregory.price@memverge.com>

CXL emulation of interleave requires read and write hooks due to
requirement for subpage granularity. The Linux kernel stack now enables
using this memory as conventional memory in a separate NUMA node. If a
process is deliberately forced to run from that node
$ numactl --membind=1 ls
the page table walk on i386 fails.

Useful part of backtrace:

     (cpu=cpu@entry=0x555556fd9000, fmt=fmt@entry=0x555555fe3378 "cpu_io_recompile: could not find TB for pc=%p")
     at ../../cpu-target.c:359
     (retaddr=0, addr=19595792376, attrs=..., xlat=<optimized out>, cpu=0x555556fd9000, out_offset=<synthetic pointer>)
     at ../../accel/tcg/cputlb.c:1339
     (cpu=0x555556fd9000, full=0x7fffee0d96e0, ret_be=ret_be@entry=0, addr=19595792376, size=size@entry=8, mmu_idx=4, type=MMU_DATA_LOAD, ra=0) at ../../accel/tcg/cputlb.c:2030      (cpu=cpu@entry=0x555556fd9000, p=p@entry=0x7ffff56fddc0, mmu_idx=<optimized out>, type=type@entry=MMU_DATA_LOAD, memop=<optimized out>, ra=ra@entry=0) at ../../accel/tcg/cputlb.c:2356      (cpu=cpu@entry=0x555556fd9000, addr=addr@entry=19595792376, oi=oi@entry=52, ra=ra@entry=0, access_type=access_type@entry=MMU_DATA_LOAD) at ../../accel/tcg/cputlb.c:2439
     at ../../accel/tcg/ldst_common.c.inc:301
     at ../../target/i386/tcg/sysemu/excp_helper.c:173
     (err=0x7ffff56fdf80, out=0x7ffff56fdf70, mmu_idx=0, access_type=MMU_INST_FETCH, addr=18446744072116178925, env=0x555556fdb7c0)
     at ../../target/i386/tcg/sysemu/excp_helper.c:578
     (cs=0x555556fd9000, addr=18446744072116178925, size=<optimized out>, access_type=MMU_INST_FETCH, mmu_idx=0, probe=<optimized out>, retaddr=0) at ../../target/i386/tcg/sysemu/excp_helper.c:604

Avoid this by plumbing the address all the way down from
x86_cpu_tlb_fill() where is available as retaddr to the actual accessors
which provide it to probe_access_full() which already handles MMIO accesses.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Gregory Price <gregory.price@memverge.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
v3: No change.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/2180
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/2220


r~




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