tests/qtest/libqos: add DMA support for writing and reading fw_cfg files

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 add 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.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
Message-ID: <20250120043847.954881-3-anisinha@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>

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 +62,60 @@ 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);
+
+    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));
+    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)
 {
@@ -121,6 +177,89 @@ 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);
+    g_assert(filename);
+    g_assert(data);
+    g_assert(buflen);
+    /* 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);
+    g_assert(filename);
+    g_assert(data);
+    g_assert(buflen);
+    /* 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;

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);