Re: [PATCH v4 2/2] tests/qtest/libqos: add DMA support for writing and reading fw_cfg files

[Ani Sinha]

> On 10 Jan 2025, at 2:00 AM, Fabiano Rosas <farosas@suse.de> wrote:
> 
> Ani Sinha <anisinha@redhat.com> writes:
> 
>> 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.
> 
> What's the blocker for the rest of the series?

The broker is that the consumer of this api is a new qtest which is written to 
test a brand new feature. I would rather post that patchset separately.
A compromise is ... 

> It would be preferable to
> merge it all together, rather than this going in first without any
> users.

In my cover letter I have pointed to the patch series that actually uses this 
api. That way those who want to check out that branch and test these changes 
can do so.

> 
>> 
>> Signed-off-by: Ani Sinha <anisinha@redhat.com>
>> ---
>> tests/qtest/libqos/fw_cfg.c | 138 ++++++++++++++++++++++++++++++++++++
>> tests/qtest/libqos/fw_cfg.h |   6 +-
>> 2 files changed, 143 insertions(+), 1 deletion(-)
>> 
>> diff --git a/tests/qtest/libqos/fw_cfg.c b/tests/qtest/libqos/fw_cfg.c
>> index f1ed4898f7..b3ae97d32d 100644
>> --- a/tests/qtest/libqos/fw_cfg.c
>> +++ b/tests/qtest/libqos/fw_cfg.c
>> @@ -14,6 +14,8 @@
>> 
>> #include "qemu/osdep.h"
>> #include "fw_cfg.h"
>> +#include "malloc-pc.h"
>> +#include "libqos-malloc.h"
>> #include "../libqtest.h"
>> #include "qemu/bswap.h"
>> #include "hw/nvram/fw_cfg.h"
>> @@ -60,6 +62,65 @@ 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, QOSState *qs, void *address,
>> +                     uint32_t length, uint32_t control)
>> +{
>> +    FWCfgDmaAccess access;
>> +    uint32_t addr;
>> +    uint64_t guest_access_addr;
>> +    uint64_t gaddr;
>> +
>> +    /* create a data buffer in guest memory */
>> +    gaddr = guest_alloc(&qs->alloc, length);
>> +    g_assert(gaddr);
> 
> Same here, none of these asserts are needed.

Ok will remove.

> 
>> +
>> +    if (control & FW_CFG_DMA_CTL_WRITE) {
>> +        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(&qs->alloc, 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));
>> +
>> +    if (control & FW_CFG_DMA_CTL_READ) {
>> +        qtest_bufread(fw_cfg->qts, gaddr, address, length);
>> +    }
>> +
>> +    guest_free(&qs->alloc, guest_access_addr);
>> +    guest_free(&qs->alloc, gaddr);
>> +}
>> +
>> +static void
>> +qfw_cfg_write_entry(QFWCFG *fw_cfg, QOSState *qs, uint16_t key,
>> +                    void *buf, uint32_t len)
>> +{
>> +    qfw_cfg_select(fw_cfg, key);
>> +    qfw_cfg_dma_transfer(fw_cfg, qs, buf, len, FW_CFG_DMA_CTL_WRITE);
>> +}
>> +
>> +static void
>> +qfw_cfg_read_entry(QFWCFG *fw_cfg, QOSState *qs, uint16_t key,
>> +                   void *buf, uint32_t len)
>> +{
>> +    qfw_cfg_select(fw_cfg, key);
>> +    qfw_cfg_dma_transfer(fw_cfg, qs, buf, len, FW_CFG_DMA_CTL_READ);
>> +}
>> +
>> static bool
>> find_pdir_entry(QFWCFG *fw_cfg, const char *filename,
>>                 uint16_t *sel, uint32_t *size)
>> @@ -123,6 +184,83 @@ 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.
>> + *
>> + * Passed QOSState pointer qs must be initialized. qs->alloc must also be
>> + * properly initialized.
>> + */
>> +size_t qfw_cfg_read_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
>> +                         void *data, size_t buflen)
>> +{
>> +    uint32_t len = 0;
>> +    uint16_t sel;
>> +    uint32_t id;
>> +
>> +    g_assert(qs);
>> +    /* 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, qs, sel, data, len);
>> +    }
>> +
>> +    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.
>> + *
>> + * Passed QOSState pointer qs must be initialized. qs->alloc must also be
>> + * properly initialized.
>> + */
>> +size_t qfw_cfg_write_file(QFWCFG *fw_cfg, QOSState *qs, const char 
>> *filename,
>> +                          void *data, size_t buflen)
>> +{
>> +    uint32_t len = 0;
>> +    uint16_t sel;
>> +    uint32_t id;
>> +
>> +    g_assert(qs);
>> +    /* 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, qs, sel, data, len);
>> +    }
>> +    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..6d6ff09725 100644
>> --- a/tests/qtest/libqos/fw_cfg.h
>> +++ b/tests/qtest/libqos/fw_cfg.h
>> @@ -14,6 +14,7 @@
>> #define LIBQOS_FW_CFG_H
>> 
>> #include "../libqtest.h"
>> +#include "libqos.h"
>> 
>> typedef struct QFWCFG QFWCFG;
>> 
>> @@ -33,7 +34,10 @@ 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, QOSState *qs, const char 
>> *filename,
>> +                          void *data, size_t buflen);
>> +size_t qfw_cfg_read_file(QFWCFG *fw_cfg, QOSState *qs, 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);
>> QFWCFG *io_fw_cfg_init(QTestState *qts, uint16_t base);