Re: [PATCH] tests/qtest/libqos: add DMA support for writing and reading fw_cfg files

[Ani Sinha]

> On 7 Jan 2025, at 6:28 PM, Ani Sinha <anisinha@redhat.com> wrote:
> 
> At present, the libqos/fw_cfg.c library does not support the modern DMA which
> is required to write to the fw_cfg files. It only uses the IO interface.
> Implement read and write methods based on DMA. This will enable developers to
> write tests that writes to the fw_cfg file(s). The structure of the code is
> taken from edk2 fw_cfg implementation. It has been tested by writing a qtest
> that writes to a fw_cfg file. This test will be part of a future patch series.
> 
> Signed-off-by: Ani Sinha <anisinha@redhat.com>

Clearly I sent this out a tad bit early.

> ---
> tests/qtest/libqos/fw_cfg.c | 150 ++++++++++++++++++++++++++++++++++++
> tests/qtest/libqos/fw_cfg.h |   4 +
> 2 files changed, 154 insertions(+)
> 
> diff --git a/tests/qtest/libqos/fw_cfg.c b/tests/qtest/libqos/fw_cfg.c
> index 89f053ccac..1b855fbb15 100644
> --- a/tests/qtest/libqos/fw_cfg.c
> +++ b/tests/qtest/libqos/fw_cfg.c
> @@ -17,6 +17,8 @@
> #include "../libqtest.h"
> #include "qemu/bswap.h"
> #include "hw/nvram/fw_cfg.h"
> +#include "malloc-pc.h"
> +#include "libqos-malloc.h"
> 
> void qfw_cfg_select(QFWCFG *fw_cfg, uint16_t key)
> {
> @@ -60,6 +62,59 @@ static void mm_fw_cfg_select(QFWCFG *fw_cfg, uint16_t key)
>     qtest_writew(fw_cfg->qts, fw_cfg->base, key);
> }
> 
> +static void
> +qfw_cfg_dma_transfer(QFWCFG *fw_cfg, void *address, uint32_t length,
> +                     uint32_t control)
> +{
> +    FWCfgDmaAccess access;
> +    uint32_t addr;
> +    QGuestAllocator guest_malloc;
> +    uint64_t guest_access_addr;
> +    uint64_t gaddr;
> +
> +    pc_alloc_init(&guest_malloc, fw_cfg->qts, ALLOC_NO_FLAGS);
> +
> +    /* create a data buffer in guest memory */
> +    gaddr = guest_alloc(&guest_malloc, length);
> +    g_assert(gaddr);
> +    qtest_bufwrite(fw_cfg->qts, gaddr, address, length);
> +
> +    access.address = cpu_to_be64(gaddr);
> +    access.length = cpu_to_be32(length);
> +    access.control = cpu_to_be32(control);
> +
> +    guest_access_addr = guest_alloc(&guest_malloc, sizeof(access));
> +    g_assert(guest_access_addr);
> +    qtest_bufwrite(fw_cfg->qts, guest_access_addr, &access, sizeof(access));
> +
> +    /* lower 32 bits */
> +    addr = cpu_to_be32((uint32_t)(uintptr_t)guest_access_addr);
> +    qtest_outl(fw_cfg->qts, fw_cfg->base + 8, addr);
> +    /* upper 32 bits */
> +    addr = cpu_to_be32((uint32_t)(uintptr_t)(guest_access_addr >> 32));
> +    qtest_outl(fw_cfg->qts, fw_cfg->base + 4, addr);
> +
> +    g_assert(!(be32_to_cpu(access.control) & FW_CFG_DMA_CTL_ERROR));
> +
> +    guest_free(&guest_malloc, guest_access_addr);
> +    guest_free(&guest_malloc, gaddr);
> +    alloc_destroy(&guest_malloc);
> +}
> +
> +static void
> +qfw_cfg_write_entry(QFWCFG *fw_cfg, uint16_t key, void *buf, int len)
> +{
> +    qfw_cfg_select(fw_cfg, key);
> +    qfw_cfg_dma_transfer(fw_cfg, buf, len, FW_CFG_DMA_CTL_WRITE);
> +}
> +
> +static void
> +qfw_cfg_read_entry(QFWCFG *fw_cfg, uint16_t key, void *buf, int len)
> +{
> +    qfw_cfg_select(fw_cfg, key);
> +    qfw_cfg_dma_transfer(fw_cfg, buf, len, FW_CFG_DMA_CTL_READ);
> +}
> +
> /*
>  * The caller need check the return value. When the return value is
>  * nonzero, it means that some bytes have been transferred.
> @@ -104,6 +159,101 @@ size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char 
> *filename,
>     return filesize;
> }
> 
> +/*
> + * The caller need check the return value. When the return value is
> + * nonzero, it means that some bytes have been transferred.
> + *
> + * If the fw_cfg file in question is smaller than the allocated & passed-in
> + * buffer, then the first len bytes were read.
> + *
> + * If the fw_cfg file in question is larger than the passed-in
> + * buffer, then the return value explains how much was actually read.
> + *
> + * It is illegal to call this function if fw_cfg does not support DMA
> + * interface. The caller should ensure that DMA is supported before
> + * calling this function.
> + */
> +size_t qfw_cfg_read_file(QFWCFG *fw_cfg, const char *filename,
> +                         void *data, size_t buflen)
> +{
> +    uint32_t count;
> +    uint32_t i;
> +    unsigned char *filesbuf = NULL;
> +    size_t dsize;
> +    size_t len = 0;
> +    FWCfgFile *pdir_entry;
> +
> +    qfw_cfg_get(fw_cfg, FW_CFG_FILE_DIR, &count, sizeof(count));
> +    count = be32_to_cpu(count);
> +    dsize = sizeof(uint32_t) + count * sizeof(struct fw_cfg_file);
> +    filesbuf = g_malloc(dsize);
> +    qfw_cfg_get(fw_cfg, FW_CFG_FILE_DIR, filesbuf, dsize);
> +    pdir_entry = (FWCfgFile *)(filesbuf + sizeof(uint32_t));
> +    for (i = 0; i < count; ++i, ++pdir_entry) {
> +        if (!strcmp(pdir_entry->name, filename)) {

This code is repeated in multiple functions. So I will refactor this into a 
helper.

> +            len = be32_to_cpu(pdir_entry->size);
> +            uint16_t sel = be16_to_cpu(pdir_entry->select);
> +            if (len > buflen) {
> +                len = buflen;
> +            }
> +            qfw_cfg_read_entry(fw_cfg, sel, data, len);
> +            break;
> +        }
> +    }
> +    g_free(filesbuf);
> +    return len;
> +}
> +
> +/*
> + * The caller need check the return value. When the return value is
> + * nonzero, it means that some bytes have been transferred.
> + *
> + * If the fw_cfg file in question is smaller than the allocated & passed-in
> + * buffer, then the buffer has been partially written.
> + *
> + * If the fw_cfg file in question is larger than the passed-in
> + * buffer, then the return value explains how much was actually written.
> + *
> + * It is illegal to call this function if fw_cfg does not support DMA
> + * interface. The caller should ensure that DMA is supported before
> + * calling this function.
> + */
> +size_t qfw_cfg_write_file(QFWCFG *fw_cfg, const char *filename,
> +                          void *data, size_t buflen)
> +{
> +    uint32_t count;
> +    uint32_t i;
> +    size_t len = 0;
> +    uint32_t id;
> +    unsigned char *filesbuf = NULL;
> +    size_t dsize;
> +    FWCfgFile *pdir_entry;
> +
> +    /* write operation is only valid if DMA is supported */
> +    id = qfw_cfg_get_u32(fw_cfg, FW_CFG_ID);
> +    g_assert(id & FW_CFG_VERSION_DMA);
> +
> +    qfw_cfg_get(fw_cfg, FW_CFG_FILE_DIR, &count, sizeof(count));
> +    count = be32_to_cpu(count);
> +    dsize = sizeof(uint32_t) + count * sizeof(struct fw_cfg_file);
> +    filesbuf = g_malloc(dsize);
> +    qfw_cfg_get(fw_cfg, FW_CFG_FILE_DIR, filesbuf, dsize);
> +    pdir_entry = (FWCfgFile *)(filesbuf + sizeof(uint32_t));
> +    for (i = 0; i < count; ++i, ++pdir_entry) {
> +        if (!strcmp(pdir_entry->name, filename)) {
> +            len = be32_to_cpu(pdir_entry->size);
> +            uint16_t sel = be16_to_cpu(pdir_entry->select);
> +            if (len > buflen) {
> +                len = buflen;
> +            }
> +            qfw_cfg_write_entry(fw_cfg, sel, data, len);
> +            break;
> +        }
> +    }
> +    g_free(filesbuf);
> +    return len;
> +}
> +
> static void mm_fw_cfg_read(QFWCFG *fw_cfg, void *data, size_t len)
> {
>     uint8_t *ptr = data;
> diff --git a/tests/qtest/libqos/fw_cfg.h b/tests/qtest/libqos/fw_cfg.h
> index b0456a15df..62221a9500 100644
> --- a/tests/qtest/libqos/fw_cfg.h
> +++ b/tests/qtest/libqos/fw_cfg.h
> @@ -33,6 +33,10 @@ uint32_t qfw_cfg_get_u32(QFWCFG *fw_cfg, uint16_t key);
> uint64_t qfw_cfg_get_u64(QFWCFG *fw_cfg, uint16_t key);
> size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char *filename,
>                         void *data, size_t buflen);
> +size_t qfw_cfg_write_file(QFWCFG *fw_cfg, const char *filename,
> +                          void *data, size_t buflen);
> +size_t qfw_cfg_read_file(QFWCFG *fw_cfg, const char *filename,
> +                         void *data, size_t buflen);
> 
> QFWCFG *mm_fw_cfg_init(QTestState *qts, uint64_t base);
> void mm_fw_cfg_uninit(QFWCFG *fw_cfg);
> -- 
> 2.45.2
>