diff options
| -rw-r--r-- | src/arch/x86/interface/pcbios/rtc_entropy.c | 76 |
1 files changed, 72 insertions, 4 deletions
diff --git a/src/arch/x86/interface/pcbios/rtc_entropy.c b/src/arch/x86/interface/pcbios/rtc_entropy.c index c400d8a78..c9e5e4617 100644 --- a/src/arch/x86/interface/pcbios/rtc_entropy.c +++ b/src/arch/x86/interface/pcbios/rtc_entropy.c @@ -55,6 +55,10 @@ static struct segoff rtc_old_handler; extern volatile uint8_t __text16 ( rtc_flag ); #define rtc_flag __use_text16 ( rtc_flag ) +/** RTC interrupt requires rearming each time */ +extern volatile uint8_t __text16 ( rtc_rearm ); +#define rtc_rearm __use_text16 ( rtc_rearm ) + /** * Hook RTC interrupt handler * @@ -73,19 +77,49 @@ static void rtc_hook_isr ( void ) { */ "movb %2, %%al\n\t" "outb %%al, %0\n\t" - "inb %1\n\t" + "inb %1, %%al\n\t" + + /* Rearm RTC interrupt, if required */ + "testb $0xff, %%cs:rtc_rearm\n\t" + "jz rtc_isr_done\n\t" + /* Preserve registers */ + "pushw %%bx\n\t" + /* Read current contents of register B */ + "movb %3, %%al\n\t" + "outb %%al, %0\n\t" + "inb %1, %%al\n\t" + "movb %%al, %%bl\n\t" + /* Toggle periodic interrupt enable in register B */ + "movb %3, %%al\n\t" + "outb %%al, %0\n\t" + "movb %%bl, %%al\n\t" + "xorb %4, %%al\n\t" + "outb %%al, %1\n\t" + /* Restore periodic interrupt enable in register B */ + "movb %3, %%al\n\t" + "outb %%al, %0\n\t" + "movb %%bl, %%al\n\t" + "outb %%al, %1\n\t" + /* Restore registers */ + "popw %%bx\n\t" + /* Send EOI */ + "\nrtc_isr_done:\n\t" "movb $0x20, %%al\n\t" "outb %%al, $0xa0\n\t" "outb %%al, $0x20\n\t" /* Restore registers and return */ "popw %%ax\n\t" "iret\n\t" + "\nrtc_flag:\n\t" + ".byte 0\n\t" + + "\nrtc_rearm:\n\t" ".byte 0\n\t" ) : - : "i" ( CMOS_ADDRESS ), "i" ( CMOS_DATA ), - "i" ( RTC_STATUS_C ) ); + : "i" ( CMOS_ADDRESS ), "i" ( CMOS_DATA ), "i" ( RTC_STATUS_C ), + "i" ( RTC_STATUS_B ), "i" ( RTC_STATUS_B_PIE ) ); hook_bios_interrupt ( RTC_INT, ( intptr_t ) rtc_isr, &rtc_old_handler ); } @@ -178,6 +212,38 @@ static int rtc_entropy_check ( void ) { } /** + * Apply workaround for broken RTC interrupts + * + * @ret rc Return status code + * + * Some versions of Hyper-V (observed with Windows Server 2022) fail + * to properly emulate the RTC periodic interrupt. The typical + * symptom is that only a single interrupt will be generated: + * subsequent interrupts will appear to be asserted by the virtual RTC + * but will be ignored by the virtual PIC. + * + * Experiments show that this apparent hypervisor bug can be worked + * around by disabling and re-enabling the periodic interrupt within + * the interrupt handler. + */ +static int rtc_entropy_workaround ( void ) { + int rc; + + /* Apply workaround */ + DBGC ( &rtc_flag, "RTC applying workaround for broken interrupts\n" ); + rtc_rearm = 1; + + /* Force one interrupt, to trigger the rearming code path */ + __asm__ __volatile__ ( "int %0" : : "i" ( RTC_INT ) ); + + /* Check that RTC interrupts are now working */ + if ( ( rc = rtc_entropy_check() ) != 0 ) + return rc; + + return 0; +} + +/** * Enable entropy gathering * * @ret rc Return status code @@ -200,8 +266,10 @@ static int rtc_entropy_enable ( void ) { rtc_enable_int(); /* Check that RTC interrupts are working */ - if ( ( rc = rtc_entropy_check() ) != 0 ) + if ( ( ( rc = rtc_entropy_check() ) != 0 ) && + ( ( rc = rtc_entropy_workaround() ) != 0 ) ) { goto err_check; + } return 0; |