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x86/xen: introduce non-hypercall based emergency print

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The current xc_printf() function uses an hypercall in order to send character
buffers to the hypervisor for it to print on the hypervisor console (if the
hypervisor is configured to print such messages).

This requires the hypercall page to be initialized, which is extra work and can
go wrong.

On x86 instead of using the console IO hypercall use the debug console IO port,
also called "port E9 hack".  This allows sending characters to Xen using an
outb instruction, without any initialization required.

Keep the previous hypervisor based implementation by using the weak attribute,
which allows each architecture to provide an alternate (arch-specific)
implementation.

Sponsored by: Cloud Software Group
Reviewed by: markj
Differential revision: https://reviews.freebsd.org/D43929
This commit is contained in:
Roger Pau Monné 2024-01-22 14:20:25 +01:00
parent 4ece79968e
commit 399386f190
3 changed files with 22 additions and 5 deletions
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15
sys/dev/xen/console/xen_console.c
View File

@ -138,6 +138,13 @@ struct putchar_arg {
size_t n_next;
};
void __weak_symbol
xen_emergency_print(const char *str, size_t size)
{
KASSERT((xen_domain()), ("call to xc_printf from non Xen guest"));
HYPERVISOR_console_write(str, size);
}
static void
putchar(int c, void *arg)
{
@ -150,12 +157,12 @@ putchar(int c, void *arg)
* We have no buffer, output directly to the
* console char by char.
*/
HYPERVISOR_console_write((char *)&c, 1);
xen_emergency_print((char *)&c, 1);
} else {
pca->buf[pca->n_next++] = c;
if ((pca->size == pca->n_next) || (c = '\0')) {
/* Flush the buffer */
HYPERVISOR_console_write(pca->buf, pca->n_next);
xen_emergency_print(pca->buf, pca->n_next);
pca->n_next = 0;
}
}
@ -177,15 +184,13 @@ xc_printf(const char *fmt, ...)
pca.size = 0;
#endif
KASSERT((xen_domain()), ("call to xc_printf from non Xen guest"));
va_start(ap, fmt);
kvprintf(fmt, putchar, &pca, 10, ap);
va_end(ap);
#ifdef PRINTF_BUFR_SIZE
if (pca.n_next != 0)
HYPERVISOR_console_write(buf, pca.n_next);
xen_emergency_print(buf, pca.n_next);
#endif
}

5
sys/x86/xen/hvm.c
View File

@ -95,6 +95,11 @@ TUNABLE_INT("hw.xen.disable_pv_nics", &xen_disable_pv_nics);
/*---------------------- XEN Hypervisor Probe and Setup ----------------------*/
void xen_emergency_print(const char *str, size_t size)
{
outsb(XEN_HVM_DEBUGCONS_IOPORT, str, size);
}
uint32_t xen_cpuid_base;
static uint32_t

7
sys/xen/xen-os.h
View File

@ -151,6 +151,13 @@ int xenmem_free(device_t dev, int res_id, struct resource *res);
/* Debug/emergency function, prints directly to hypervisor console */
void xc_printf(const char *, ...) __printflike(1, 2);
/*
* Emergency print function, can be defined per-arch, otherwise defaults to
* HYPERVISOR_console_write. Should not be called directly, use xc_printf
* instead.
*/
void xen_emergency_print(const char *str, size_t size);
#ifndef xen_mb
#define xen_mb() mb()
#endif