Re: [PATCH v2] tests/qtest/libqos: add DMA support for writing and reading fw_cfg files

[Ani Sinha]

> On 7 Jan 2025, at 8:21 PM, Ani Sinha <anisinha@redhat.com> wrote:
> 
> At present, the libqos/fw_cfg.c library does not support the modern DMA
> interface 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>

Please disregard this patch for now. I was under the false impression that this 
was working. More testing revealed that there might still be some issues with 
this patch. Apologies for this.

> ---
> tests/qtest/libqos/fw_cfg.c | 191 +++++++++++++++++++++++++++++++-----
> tests/qtest/libqos/fw_cfg.h |   4 +
> 2 files changed, 172 insertions(+), 23 deletions(-)
> 
> changelog:
> v2: refactor common code into a helper.
> 
> diff --git a/tests/qtest/libqos/fw_cfg.c b/tests/qtest/libqos/fw_cfg.c
> index 89f053ccac..ac4c6b73e5 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 +62,94 @@ 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);
> +
> +    /* now create a separate buffer in guest memory for 'access' */
> +    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));
> +
> +    /* write lower 32 bits of address */
> +    addr = cpu_to_be32((uint32_t)(uintptr_t)guest_access_addr);
> +    qtest_outl(fw_cfg->qts, fw_cfg->base + 8, addr);
> +
> +    /* write upper 32 bits of address */
> +    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, uint32_t 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, uint32_t len)
> +{
> +    qfw_cfg_select(fw_cfg, key);
> +    qfw_cfg_dma_transfer(fw_cfg, buf, len, FW_CFG_DMA_CTL_READ);
> +}
> +
> +static bool find_pdir_entry(QFWCFG *fw_cfg, const char *filename,
> +                            uint16_t *sel, uint32_t *size)
> +{
> +    unsigned char *filesbuf = NULL;
> +    uint32_t count;
> +    size_t dsize;
> +    FWCfgFile *pdir_entry;
> +    uint32_t i;
> +    bool found = false;
> +
> +    *size = 0;
> +    *sel = 0;
> +
> +    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);
> +    g_assert(filesbuf);
> +    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)) {
> +            *size = be32_to_cpu(pdir_entry->size);
> +            *sel = be16_to_cpu(pdir_entry->select);
> +            found = true;
> +            break;
> +        }
> +    }
> +
> +    g_free(filesbuf);
> +    return found;
> +}
> +
> /*
>  * The caller need check the return value. When the return value is
>  * nonzero, it means that some bytes have been transferred.
> @@ -73,37 +163,92 @@ static void mm_fw_cfg_select(QFWCFG *fw_cfg, uint16_t 
> key)
>  * populated, it has received only a starting slice of the fw_cfg file.
>  */
> size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char *filename,
> -                      void *data, size_t buflen)
> +                        void *data, size_t buflen)
> {
> -    uint32_t count;
> -    uint32_t i;
> -    unsigned char *filesbuf = NULL;
> -    size_t dsize;
> -    FWCfgFile *pdir_entry;
>     size_t filesize = 0;
> +    uint32_t len;
> +    uint16_t sel;
> 
> -    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)) {
> -            uint32_t len = be32_to_cpu(pdir_entry->size);
> -            uint16_t sel = be16_to_cpu(pdir_entry->select);
> -            filesize = len;
> -            if (len > buflen) {
> -                len = buflen;
> -            }
> -            qfw_cfg_get(fw_cfg, sel, data, len);
> -            break;
> +    if (find_pdir_entry(fw_cfg, filename, &sel, &len)) {
> +        filesize = len;
> +        if (len > buflen) {
> +            len = buflen;
>         }
> +        qfw_cfg_get(fw_cfg, sel, data, len);
>     }
> -    g_free(filesbuf);
> +
>     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 len = 0;
> +    uint16_t sel;
> +    uint32_t id;
> +
> +    /* check if DMA is supported since we use DMA for read */
> +    id = qfw_cfg_get_u32(fw_cfg, FW_CFG_ID);
> +    g_assert(id & FW_CFG_VERSION_DMA);
> +
> +    if (find_pdir_entry(fw_cfg, filename, &sel, &len)) {
> +        if (len > buflen) {
> +            len = buflen;
> +        }
> +        qfw_cfg_read_entry(fw_cfg, sel, data, len);
> +    }
> +
> +    return (size_t) 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 len = 0;
> +    uint16_t sel;
> +    uint32_t id;
> +
> +    /* 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);
> +
> +    if (find_pdir_entry(fw_cfg, filename, &sel, &len)) {
> +        if (len > buflen) {
> +            len = buflen;
> +        }
> +        qfw_cfg_write_entry(fw_cfg, sel, data, len);
> +    }
> +    return (size_t) 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
>